Cilic still has plenty left in the tank

Marin Cilic is ranked No. 19 in the world

It has been four and a half years since Marin Cilic broke into the top 10 on the ATP, and his run in the top 10 lasted just nine weeks only to never return. So it is easy to forget that the Croat is only 25-years old - two years younger than the average player in the top 100. Even four and a half years removed from his career-high ranking, Cilic still hasn't reached his peak yet. 

Last year, Cilic was suspended for nine months from tennis after testing positive nikethamide. His suspension was eventually reduced to four months after an appeal, allowing Cilic to return to the tour at the start of 2014.

The Croat rejoined the tour with a ranking of 37 and a new coach. Goran Ivanisevic, a fellow Croat and former world No. 2, joined Cilic's team, looking to help him return to the top 10 after four years. Ivanisevic, who is the only player in tennis history to have struck over 10,000 aces, made an immediate impact on Cilic's game - Cilic was serving like his coach.

After years of tossing the ball behind his head and bending his back to reach the toss for a simple kick serve, Cilic began tossing the ball out in front of him and hitting it much flatter. And the difference showed up in the stats immediately.

Cilic averaged six aces per 10 service games in his career going into the 2014 season, but in 2014, that number is up from six to nine. He has seen similar increases in percentage of first serves made and won, allowing him to hold serve 85% of the time. In March, Cilic faced world No. 2 Novak Djokovic, who is known for his ability to get serves back in play, but Cilic still fired 13 aces in 12 service games.

His serve has improved so much that even though he has been breaking serve at his lowest rate since 2008, he is still seeing some of his best results in tournaments.

Cilic reached the final in Delray Beach without 
dropping a set and then beat
Kevin Anderson 7-6(6), 6-7(7), 6-4 in the final.

In February, Cilic won a pair of hard court titles and reached the final of Rotterdam. The final in Rotterdam was just the third time in his career that he reached the final of a 500-point event. That, to go along with two titles in one month, something he had only done three times in an entire season.

Cilic has continued to post solid results in 2014, reaching the round of 16 at consecutive North American hard court Masters events in the past two weeks. He also reached the semifinals in Umag and quarterfinals in Barcelona.

The one stumbling block for Cilic in 2014 has been Djokovic. Despite winning the first set against the Serb 6-1 in Indian Wells, Djokovic came roaring back to claim the match. The pair were drawn to meet again in the round of 32 at Roland Garros, where again Cilic took a set, but Djokovic took the match.

Cilic defeated world No. 6 Tomas Berdych en route to his
first career quarterfinal at Wimbledon this year.

At Wimbledon, Cilic reached his first grand slam quarterfinal since the 2012 US Open. And once again, it was Djokovic on the other side of the net. After splitting the first two sets, Cilic won the tightly contested third set in a tiebreaker, 7-4. However, Cilic's serve wilted away in the final two sets, getting broken four times, ending his run at Wimbledon and his chance to reach just a second major semifinal.

Cilic is now ranked No. 19 in the world, but has zero points left to defend in 2014 with some of his favorite events left on the calendar. The rest of the year is nothing but hard courts, where Cilic has won 77% of his matches this season. And many of those hard court events are indoors, where the Croat has won 86% of his matches in 2014.

Cilic is currently No. 13 in the Race Rankings, trailing No. 8 Andy Murray by less than 800 points. With his favorite part of the season left, Cilic could make a run for the top eight in the Race Rankings and a spot in the year-end finals.

Myth vs. Math: Big Servers in Tiebreakers

This is the first installment in a five-part series called Myth vs. Math. In this series, I am going to take a look at five widely-accepted statements that tennis writers, analysts, fans, and commentators frequently make. I'm going to take these statements and see how they hold up against the numbers. The first statement in this series is "big servers have a notable advantage in tiebreakers."

The Myth

In tennis, the serve is an absolutely essential part of every player's game. It's the shot that starts every point. Having a big serve like Goran Ivanisevic, Andy Roddick, or Ivo Karlovic can be a huge weapon for getting out of trouble. However, having a weak serve means working a lot harder to win service games.

Anytime one of the big servers reaches a tiebreaker against a player, who relies more on other parts of their game, someone is bound to claim that the bigger server has the advantage. Before tiebreakers, when a commentator asks the other who they are picking to win the tiebreaker, the response is often something along the lines of "John Doe has the bigger serve, so I would have to give him the advantage in this tiebreaker."

And these kind of statements seem to make sense. Sets involving big servers have a higher probability of reaching a tiebreaker, so the big servers have more experience in those situations. Also, taking care of the points on serve is particularly crucial when one mini-break can determine a set.

However, does that mean the big servers actually have an advantage? Every point in a tiebreaker matters, whether it is on serve or not. And the big servers tend to be weak returners. So is being a big server really an advantage in a tiebreaker, or does it just make up for a weak return game?

The Math

The statistical mark of any big server is aces. So what I want to see is how high the correlation between aces and tiebreak win percentage is. If there is a high correlation, then the claim is true, but if there isn't a notable correlation, then the math

The ATP began tracking aces back in 1991. Since then, 42 players have played at least 600 tour-level matches. I used those 42 players as my sample to create this scatterplot.

On the x-axis is the players' aces per match, while the y-axis is each players' win percentage in tiebreaks multiplied by 50. I multiplied it by 50 simply to make the range of the two sets of data equivalent to each other. Each 'x' on the scatterplot represents one of the 42 players. The line through the middle of the data is a linear least squares fit. It shows for an average player how much an increase in aces per match will increase the chance of winning a tiebreaker.
 

To make this a little more tangible, let's look at how individual players fit on the scatterplot. The 'x' furthest to the right of the graph is Goran Ivanisevic, who won 58.9% of his tiebreakers, which is better than expected for a player with over 13 aces per match. The 'x' is the upper-left is Rafael Nadal, who strikes an average of just under three aces per match, but still wins 63.8% of his tiebreakers. At the bottom of the graph is Vincent Spadea, who won just 41.9% of his tiebreakers, while hitting 3.5 aces per match. The 'x' that is closest to sitting perfectly on the line is Tim Henman, who hit 5.9 aces per match, while winning 53.6% of his tiebreakers.

 

The slope of the linear regression is very mild, indicating that while there is a connection between aces and winning percentage in tiebreakers, it is very week. The correlation coefficient is merely .277, which means that aces per match are just 7.69% predictive of the outcome of a tiebreak.

 

Flaws in the Math

 

First, the scatterplot does nothing to account for differences in surface. This scatterplot treats all surfaces as equal. If it were broken down by surface, we may find that the statement is more true on a particular surface than another. However, the plot does show that overall, the connection is hardly impressive.

Second, in every point, there are two kinds of serves: 1st and 2nd serve. However, aces are primarily a first serve statistic since aces are so rare off the second serve. The biggest servers though are able to get a substantial amount of unreturned serves on the second delivery. A comparison of unreturned serves to tiebreak win percentage would produce a more accurate scatterplot. However, stats on unreturned serves aren't tracked at every match.
 

Third potential flaw is the sample size. Since I only looked at players with over 600 career matches played, I looked only at players who won often enough to play 600 matches. As a result, the majority of the players in the scatterplot had a winning record. In fact, the average win percentage in tiebreakers of the 42 players 54%. A look at more players with a losing record in tiebreakers could create a more complete scatterplot

 

Conclusion

Math seems to disprove the claim that "big servers have a notable advantage in tiebreakers." Having a big serve does seem to be a slight benefit in tiebreakers, but it is not much of a factor in determining the winner of a tiebreaker.
 

Supporters of the claim will often point to John Isner, who averaged exactly 16 aces per match after reaching the semifinals in Indian Wells and has a 65% winning mark in tiebreakers. However, the data shows that Isner's stats are an outlier and not indicative of other players. So perhaps the reason for Isner's success in tiebreakers has to do with something more than just having a monstrous serve.
 

So the widely-accepted claim that having a big serve is an advantage in tiebreakers should be a rejected claim.