Category Archives: Novak Djokovic

Novak Djokovic and a First-Serve Key to the Match

Landing lots of first serves is a good thing, right? Actually, how much it matters–even whether it matters–depends on who you’re talking about.

When I criticized IBM’s Keys To the Match after last year’s US Open, I identified first-serve percentage as one of three “generic keys” (along with first-serve points won and second-serve points won) that, when combined, did a better job of predicting the outcome of matches than IBM’s allegedly more sophisticated markers.  First-serve percentage is the weakest of the three generic keys–after all, the other two count points won which, short of counting sets, is as relevant as you can get.

First-serve percentage is a particularly appealing key because it is entirely dependent on one player. While a server may change his strategy based on the returning skills of his opponent, the returner has nothing to do with whether or not first serves go in the box.  Unlike the other two generic targets and the vast majority of IBM’s keys, a first-serve percentage goal is truly actionable: it is entirely within one player’s control to achieve.

In general, first-serve percentage correlates very strongly with winning percentage.  On the ATP tour from 2010 to 2013, when a player made exactly half of his first serves, he won 42.8% of the time. At 60% first serves in, he won 47.0% of the time. At 70%, the winning percentage is 57.4%.

This graph shows the rates at which players win matches when their first-serve percentages are between 50% and 72%:

1svAs the first-serve percentage increases on the horizontal axis, winning percentage steadily rises as well.  With real-world tennis data, you’ll rarely see a relationship much clearer than this one.

Different players, different keys

When we use the same approach to look at specific players, the message starts to get muddled.  Here’s the same data for Novak Djokovic, 2009-13:

nd1sv

While we shouldn’t read too much into any particular jag in this graph, it’s clear that the overall trend is very different from the first graph. Calculate the correlation coefficient, and we find that Djokovic’s winning percentage has a negative relationship with his first-serve percentage. All else equal, he’s slightly more likely to win matches when he makes fewer first serves.

Djokovic isn’t alone in displaying this sort of negative relationship, either. The three tour regulars with even more extreme profiles over the last five years are Marin Cilic, Gilles Simon, and the always-unique John Isner.

Isner regularly posts first-serve percentages well above those of other players, including 39 career matches in which he topped 75%. That sort of number would be a near guarantee of victory for most players–for instance, Andy Murray is 32-3 in matches when he hits at least 70% of first serves in–but Isner has only won 62% of his 75%+ performances.  He is nearly as good (57%) when landing 65% or fewer of his first serves.

Djokovic, Isner, and this handful of others reveals a topic on which the tennis conventional wisdom can tie itself in knots. You need to make your first serve, but your first serve also needs to be a weapon, so you can’t take too much off of it.

The specific implied relationship–that every player has a “sweet spot” between giving up too much power and missing too many first serves–doesn’t show up in the numbers. But it does seem that different players face different risks.  The typical pro could stand to make more first serves. But a few guys find that their results improve when they make fewer–presumably because they’re take more risks in an attempt to hit better ones.

Demonstrating the key

Of the players who made the cut for this study–at least 10 matches each at 10 different first-serve-percentage levels in the last five years–9 of 21 display relationships between first-serve percentage and winning percentage at least as positive as Isner’s is negative.  The most traditional player in that regard is Philipp Kohlschreiber. His graph looks a bit like a horse:

pk1sv

More than any other player, Kohli’s results have a fairly clear-cut inflection point. While it’s obscured a bit by the noisy dip at 64%, the German wins far more matches when he reaches 65% than when he doesn’t.

Kohlschreiber is joined by a group almost as motley as the one that sits at the other extreme. The other players with the strongest positive relationships between first serve percentage and winning percentage are Richard Gasquet, Murray, Roger Federer, Jeremy Chardy, and Juan Martin del Potro.

These player-specific findings tell us that in some matchups, we’ll have to be a little more subtle in what we look for from each guy. When Murray plays Djokovic, we should keep an eye on the first-serve percentages of both competitors–the one to see that he’s making enough, and the other to check that he isn’t making too many.

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Filed under Keys to the match, Novak Djokovic, Research

Novak Djokovic’s Amazing, Challenging Season End

You’ve probably heard the stats by now.  Novak Djokovic ended the 2013 season on a 24-match winning streak.  13 of his last 20 matches–all wins, of course–came against fellow members of the top ten.

Carl Bialik argues that Djokovic’s latest exploits, taken as part of his career as a whole, force us to consider him as an all-time great, in line with the seven other players who have won six to eight Grand Slam titles.  It’s a convincing case.  While Novak remains well behind Roger Federer and Rafael Nadal in most of the usual GOAT-debate categories, those are some awfully high standards to meet.  In any other era, he wouldn’t be burdened with such impossible comparisons.

Djokovic’s season-ending streak is notable in itself.  Since 1983, only three other players have won 13 or more consecutive matches against members of the top ten: Federer (24, starting at the end of 2003, among other streaks), John McEnroe (15, in early 1984), and Nadal (13, from 2012 Monte Carlo to 2013 Monte Carlo).

Djokovic’s status among the all-time greats gets a boost when you realize that this isn’t his first such streak. Coinciding with the streak, Novak won 13 consecutive contests against top-ten players in the first five months of 2011.

What makes his most recent run all the more impressive is that he has done it with so few pauses for breath.  11 of his last 14 matches were against top tenners, as were 13 of his last 19.  By contrast, Nadal’s otherwise comparable top-ten winning streak spread over 50 matches.

In fact, the tail end of Novak’s 2013 season was one of the most challenging on record.  Since 1983, only seven men played more than half of a 20-match span against top-tenners.  Federer, Nadal, and Djokovic head the list, as usual; the others are McEnroe, Andre Agassi, Pete Sampras, and Nikolay Davydenko.  Aside from Djokovic this fall, Agassi is the only one of the seven who has played 13 or more top-ten opponents in a 20-match span.  And unlike Novak, Agassi wasn’t perfect.  In his demanding stretch at the end of 1994, he lost to Goran Ivanisevic in Stockholm and to Sampras in the semis of the Tour Finals.

The nature of Djokovic’s season-ending winning streak emphasizes his stature among the sport’s greats.  In an era when a handful of contenders so thoroughly dominate the rest of the field, that small group of players is constantly facing one another.  While I don’t envy anyone playing the likes of Ivanisevic indoors, even that fearsome thought pales next to the Nadal-led gauntlet that Novak has spent the last three months navigating.

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Rafael Nadal, Top Twosomes, and the Future

The only match that either Rafael Nadal or Novak Djokovic lost in London was the final, when Nadal fell to Djokovic.  It was a good summary of the season as a whole.  The top two weren’t undefeated for the entire season, but they might as well have been.

Between them, Rafa and Novak lost only 16 matches this year, six of them to each other.  Fittingly, they split those six matches.  No single player poses a serious threat to their dominance.  Only Juan Martin del Potro defeated both this year, and he lost his five other encounters with the top-ranked duo.  The injured Andy Murray remains only a wildcard, having split Grand Slam finals with Djokovic this year but without having played Nadal since 2011.

Barring a huge upset loss in Davis Cup, Djokovic will end the season with the best-ever winning percentage for a #2-ranked player.  His 88.9% just edges out the 88.7% posted by Nadal in 2005, when he finished second to Roger Federer.  In the last thirty years, only five other #2’s won at least 85% of their matches.

Taking these six prior pairs as the best single-year twosomes the ATP has recently produced, it’s surprising to see what happened to them the following year.  In three of those seasons, neither of the ultra-dominant duos finished the next season at #1.  A third player overcame them both.

Here is the list of the seven most dominant twosomes of the last thirty years, along with their year-end rankings 12 months after the end of their notable seasons (Nx):

Yr  #1              W-L    Nx  #2              W-L    Nx  
83  John McEnroe    62-9    1  Mats Wilander   74-11   4  
85  Ivan Lendl      83-7    1  John McEnroe    72-10  14  
87  Ivan Lendl      70-7    2  Stefan Edberg   76-12   5  
89  Ivan Lendl      80-7    3  Boris Becker    58-8    2  
05  Roger Federer   81-4    1  Rafael Nadal    79-10   2  
12  Novak Djokovic  75-12   2  Roger Federer   74-13   6  
13  Rafael Nadal    76-7    ?  Novak Djokovic  72-9    ?

In 1988, Mats Wilander overcame both Ivan Lendl and Stefan Edberg to claim the #1 position.  In 1990, it was Edberg who leapfrogged Lendl and Boris Becker.  This year, of course, Nadal reclaimed the top spot from last year’s top two of Djokovic and Federer.

Those of us who watched the Tour Finals for the last week might find it hard to imagine that anyone–certainly not any of the other six men in London–would outperform either Rafa or Novak over the course of a season.  But injuries strike, slumps take hold, and–unlikely as it may seem in 2013–young players emerge and dominate. For all of the radical changes in the game since the late 80s, these precedents serve as an important reminder of the unpredictability of tennis.

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Filed under Forecasting, Novak Djokovic, Rafael Nadal, Rankings

Novak Djokovic and Neutralizing the Second Serve

When Novak Djokovic stands on the other side of the court, you’d better make some first serves.

Djokovic is one of only two players this year to win more than 55% of second-serve-return points (David Ferrer is the other).  When you consider that he also wins more than 35% of first-serve-return points, it’s less clear that the server has much of an advantage.  In fact, when Novak is performing at that level, if his opponent goes through a bad patch and only makes a quarter of his first serves, Djokovic has a better than 50% chance of breaking serve.

Commentators often refer to Djokovic’s return as a weapon, and they’re not joking.  Only six players (including Novak himself and, invariably, John Isner) won as many second-serve points as Novak won second-serve-return points.

What’s most remarkable about his return game is how quickly he neutralizes the second serve, often using tactics that, in the hands of lesser mortals, would be more appropriate for service points.  Unlike other returners, he is somewhat more likely to win a short return point than a long one.  While other players need a few shots to negate the advantage conferred by serving, Djokovic is most effective early in service points.

This graph shows the percentage of second-serve-return points won by Djokovic, by rally length, in four matches I’ve charted (US Open vs Stanislas Wawrinka and Rafael Nadal; Tour Finals vs Wawrinka and Juan Martin del Potro), compared to the the same percentage for other top-ten players (excluding Rafael Nadal) in 19 other matches I’ve charted from the US Open and Tour Finals this year:

novak1

When the return lands in play, Djokovic wins almost 53% of return points, while the pack manages less than 44%.  (All of these matches are between top-ten opponents, so the averages are much lower than season numbers, which are affected by matches against lesser opponents.)  The difference stays about the same when we take out 2- and 3-shot rallies.

When we limit our view to points that reach six shots, Novak still has a substantial edge, roughly 48% to 42%.  But in points longer than seven shots, there’s virtually no difference.

Djokovic’s return is so good that if his opponent misses his first serve, the point has turned into a Novak service point.  Opponents are forced to fight their way into their own service points!

This was particularly true in the Djokovic-Nadal US Open final.  (Follow the link, then click the ‘Serve Influence’ tab for a shot-by-shot winning percentage breakdown.)  Nadal won barely half of his second-serve points when Djokovic got his return in play, but once the rally reached five shots (or six, or seven, and so on), Nadal had the edge, winning 60% of points.  From the five-shot mark, Rafa’s advantage only increased.

Of course, Nadal won that match.  It’s not quite so useful to convert return points into service against an opponent whose own return of serve is so effective.  To win today, Novak needs to do more than just attack Rafa’s second serve.  He must either do so even more effectively than he did in New York, or put himself in a better position to win longer return points after the effect of his return has worn off.

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Filed under Match charting, Novak Djokovic, Serve statistics, World Tour Finals

Round Robin Shutouts

At this year’s World Tour Finals, we were spared the knottiest sort of round robin tiebreakers.  Each group had a clear winner (Rafael Nadal and Novak Djokovic) who went undefeated, along with another player (David Ferrer and Richard Gasquet) who failed to win a single match.

Since 1987, 33 players have recorded a 3-0 record in Tour Finals round-robin play.  This year is the first time since 2010 (Nadal and Roger Federer) that two players have done so, and before that, we have to go back to 2005 (Federer and Nikolay Davydenko).  It’s not that rare of an event–this year is the 11th time since 1987 that two players have beaten every opponent in their group.

Undefeated players are hardly guaranteed further advances, however.  Those 33 undefeated competitors have a mere 17-16 record in the semifinals, and the 17 men who reached the final won the title only nine times, against nine final-round losses.  (Twice, two undefeated players faced off in the finals–the aforementioned 2010 event along with 1993, when Michael Stich and Pete Sampras contested the title.)

The tiny sample of three round-robin matches pales in predictive value next to the old standby of ATP ranking.  In the last 26 years, the higher-ranked player has won 16 finals.  In the more top-heavy 21st century, the title has gone to the man with the superior ranking 11 of 13 times.  (Advantage: Nadal.)

That said, the gap between the two finalists is traditionally greater than it is expected to be tomorrow.  (If Stanislas Wawrinka upsets Novak Djokovic in the second semifinal, you can disregard this paragraph.  Sorry, Stan, but I’m betting against you.)  Only twice in the round-robin era have the top two players in the ATP rankings met in the concluding match of the Tour Finals–2010 (again) and 2012 (Djokovic d. Federer).

Not a shutout, but shut out

Exactly as many players–33 through 2012–have gone 0-3 in the round robin as the number who did the opposite.  Ferrer and Gasquet find themselves in quality company.

Ferrer is the 7th player ranked in the top three to lose three round robin matches.  In 2001, #1 Gustavo Kuerten was winless, only a year after claiming the championship.  Jim Courier (1993), Juan Carlos Ferrero (2003), and Nadal (2009) went 0-3 from a #2 ranking, while Thomas Muster (1995) and Djokovic (2007) did so while ranked #3.

Ferrer is notable for another dubious achievement: going 0-3 twice.  He previously did so in 2010, so this year, he matches the mark of Michael Chang, the only other man in the round-robin era to post multiple 0-3s, having gone winless in both 1989 and 1992.

His age may work against him, but there is a glimmer of hope for Ferrer.  Four players (including Kuerten, mentioned above) have gone 0-3 at one Tour Finals and won the title at another.  Andre Agassi was winless in 1989, then won the event in 1990.  Stich was 0-3 in 1991, then claimed the title in 1993.  As we’ve seen, Djokovic failed to win a single match in 2007, yet came back to win the tournament in 2008.  (Then did so again last year.)

If Nadal wins tomorrow, we can add one more name to this list, in his case finally adding the trophy to his collection four years after suffering through a winless week.  His 4-0 record so far this week may be no guarantee of success in the final, but it will hardly count against him.

Match reports: I charted today’s Federer-Nadal semifinal, as well as yesterday’s Federer-del Potro match.  Click the links for exhaustive serve, return, and shot statistics.

Worth a read: Carl Bialik analyzes ATP rematches–pairings like Fed-Delpo that faced off in back-to-back weeks.  As usual, we have to rewrite the rules for Rafa.

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Filed under David Ferrer, Forecasting, Novak Djokovic, Rafael Nadal, Records, World Tour Finals

Rafael Nadal d. Novak Djokovic: Recap and Detailed Stats

There are a lot of words that can be used to describe Novak Djokovic, but “sloppy” usually isn’t one of them.  Despite plenty of brilliance from the Serbian, he made far too many mistakes to win today.  Of course, the man on the other side of the net, Rafael Nadal, may be the best in game at forcing his opponent to attempt low-percentage shots out of pure desperation.

This morning, I predicted that, in order to win the match, Nadal would need to serve well, piling up more quick service points than usual, as Djokovic is a master of neutralizing the server’s advantage.  Give him a few shots, and it doesn’t matter who delivered the serve or how well they hit it.

That isn’t what happened.  Nadal won fewer than one in five service points on or before his second shot.  (Djokovic did a little better by that metric, but at 21%, not by much.)  Instead, Rafa won the way Novak usually does: by neutralizing his opponent’s serve.

Rafa won 45% of return points today, a mark he has never before reached against Djokovic on hard courts.  Even more importantly, he won return points at the same rate when Djokovic was serving at 30-30 or later.  Djokovic won what would normally be an impressive number of return points: 38%.  In recent years on hard courts, that was always enough to beat the Spaniard.

It was a different kind of hard-court match today, one that was decided in grueling rallies.  20% of points played today reached at least ten strokes, and Rafa won 59% of them.  Of points that finished more quickly, Djokovic simply gave away too many.  By my unofficial (and rather strict) count, he hit over 60 unforced errors, more than double Nadal’s total.

Too many of those sloppy shots came at crucial moments.  A bad forehand miss on a mid-court sitter gave Nadal set point in the third set, which Rafa converted on the first try.  Serving down a break in the fourth at 1-4, Djokovic quickly went up 30-30, then missed his second shot on three straight points to give Nadal another break point.  At 30-0 in that game, it was possible to imagine Novak clawing his way back.  Once the double break was sealed, the match was over.

Djokovic showed plenty of brilliance, especially in the second and third sets, and contributed to some incredible tennis moments, including ten rallies that exceeded 20 shots.  Indeed, Djokovic converted a break chance by claiming the best of those, a 54-stroke slugfest in the second set (video here).  He didn’t go quietly until that dreadful game at 1-4.

By beating Djokovic at his own game, Nadal solidified his status as the most dominant player on hard courts.  His undefeated record on the surface this year didn’t leave that in much doubt, but it had been three years since he won a hard-court Grand Slam.  Assuming he stays healthy, even Rafa might agree that he heads to Australia as the player to beat.

Here are the complete point-by-point stats from the match.

Here is a complete win-probability graph, as well.

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Filed under Match charting, Match reports, Novak Djokovic, Rafael Nadal, U.S. Open

Djokovic-Nadal XXXVII: The (Actual) Keys to the Match

Both Rafael Nadal and Novak Djokovic have had easy routes to the US Open final.  Neither was tested before the semifinals, and neither has yet to play a top-eight opponent.  Yet both were pushed further than expected in their last matches.  Djokovic nearly lost in another tough five-setter against Stanislas Wawrinka, and Nadal looked almost human at times, spraying errors in his match with Richard Gasquet.

For all that, the field is down to the final two.  They’ve played 36 times before, with Nadal leading the career matchup 21-15. On hard courts, it is the 18th meeting, with Djokovic leading 11-6.  It is their eleventh encounter in a Grand Slam, of which Rafa has won seven of the previous ten, while they’ve split their two previous US Open finals.

Based on the most relevant pieces of this head-to-head–the last seven Djokovic-Nadal matches on hard courts, dating back to the 2010 US Open–we can identify some clear trends that tell us what to watch for, and what each player must do to seal the US Open title.

The key: Rafa’s service games

Of these last seven hard-court matches, Nadal has won three and Djokovic has won four.  If we could find some statistical indicators that each player reached when they won and failed to accomplish when they lost, we might be on to something.  Think of it like IBM’s Keys to the Match, but with actual predictive value.

Sure enough, there are plenty of indicators that fit the bill, and they almost all center on Nadal’s serve:

  • In four of the matches, Nadal has served fewer than 5% aces.  In the other three, at least 7% aces.  He lost all four of the former, and won all three of the latter.
  • In four of the matches, Nadal won fewer than 70% of his first-serve points.  In the other three, he won at least 71%.  He lost all four of the former, and won all three of the latter.
  • In three of the matches, Nadal won fewer than 47% of his second-serve points.  In the other four, won at least 56%.  He lost all of the former, and won all but one (the 2011 Indian Wells final) of the latter.

We can sum up the importance of Nadal’s service games from a more Djokovic-centered perspective:

  • In three of the matches, Djokovic won no more than 33% of return points.  In the other four, he won at least 37% of return points.  Care to guess which matches he won?

Djokovic’s service non-indicators

The numbers are not nearly so clear for Djokovic’s service games.  In the two meetings when Novak hit the most aces, Rafa won.  In three of the only four matches when Djokovic made 62% or more of his first serves, Rafa won.  (These are starting to sound like some of the more inane of the IBM keys.)

Generally, winning 65% of first serves is good enough for Novak to beat Nadal, except for last month’s match in Canada, when he won 71% of first serves and lost in a third-set tiebreak.  In Djokovic’s worst second-serve performance of the seven matches, the 2011 US Open final, he barely won 44% of those points, yet won the match.

Of course, this doesn’t mean that Djokovic’s service stats don’t matter.  It’s no accident that Novak’s first-serve percentages were much higher in the three sets he won against Wawrinka than in the two sets he lost.  On the contrary, Djokovic’s serve just isn’t as potentially dominant as Nadal’s is.

For example, in Saturday’s semifinals, Nadal won 36% of his service points on or before his second shot, while Djokovic won only 24% of his service points that way.  Nadal’s number isn’t staggeringly high (for example, both Kevin Anderson and Marcos Baghdatis topped 40% in that category in their second-round match) but it’s a number he can earn only when serving well.  When he isn’t earning those cheap, quick points against Djokovic, Novak takes away the server’s advantage, threatening to break in almost every service game.

By contrast, Djokovic–like Victoria Azarenka–doesn’t consistently earn that type of advantage on serve.  Sure, he gets some free points that way, but in general, he takes the slight advantage that serving confers and uses that as an edge in a longer rally.  In the semifinal against Wawrinka, his average service point–including aces and unreturnables–lasted more than five shots.

Getting one number for Novak

Individually, Djokovic’s service stats don’t tell us much.  But if we consolidate them into one number–Nadal’s return points won–we get a little better clue of what beating Novak requires.  In the three matches where Nadal failed to win 34% of return points, he lost.  In the two matches where he won at least 42% of return points, he won.

But if you’re counting, you’ve surely noted that I left out two matches.  In Montreal last month, Nadal won only 34.7% of return points, and won.  In the 2011 US Open final, he won 41.7% of return points, yet lost.  Djokovic can be so effective in his own return games–or simply unbeatable when given break point opportunities, like he was that day–that even a masterful return performance like Nadal displayed in that final isn’t always good enough.

So Novak’s numbers just aren’t as indicative as his opponent’s.  Instead, keep your eyes on Rafa’s serve statistics.  Despite the many long, gut-busting rallies we can expect this afternoon, Nadal has this match–like his previous hard-court meetings with the world #1–on his own racquet.

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