Serena Williams: The Decline?

Serena Williams has been, without a doubt, the best women’s tennis player in the past few years. In 2012 and 2013 combined, she racked up a win-loss record of an astonishing 136-8. She won no fewer than 18 titles in the 28 tournaments that she entered during that period. It is one of the most dominant periods for any woman in the history of tennis.

However, there have been indications in 2014 that she is beginning to slow down. It is no surprise – keeping the incredibly high level that she had been playing at was never going to be easy and she is not getting any younger. At 33-years old, she is the third oldest woman in the WTA top 100 and is the oldest world number one in history. She is the second oldest woman to win a Grand Slam singles title, only behind Martina Navratilova. She is performing at a higher level than virtually any woman of her age has ever done before.

While she is still the world number one, her advantage over the rest of the field has fallen slightly in 2014. At the end of 2013, she had 13,260 ranking points, giving her an enormous 5,214 lead over Victoria Azarenka. At the current moment in time, she currently has 7,146 ranking points and a lead of just 466 points, which could even be smaller come the end of the week. She has a record of 48-7 in 2014 thus far, which the rest of the field would die for, but which is relatively poor by her standards. Her six titles in 15 tournaments is also a drop for her.

So, things would suggest that Serena has not enjoyed such a good year, but can we pinpoint where exactly the decline in her results and performances might have come. To achieve this, we shall look at her statistical performance and compare it with 2013. The table below shows some basic statistics. For an more effective comparison, we shall focus on her primary surface – hard courts.

Statistic	2014	2013
% Won on 1st Serve	75.4%	75.1%
% Won on 2nd Serve	51.4%	49.6%
% Won on Return	46.7%	49.7%
BP Created/Game	0.88	0.90
BP Conversion Rate	102.7	112.6
DF/Game	0.38	0.28
Aces/Game	0.84	0.64
BP Faced/Game	0.46	0.46
BP Save Rate	92.5	100.7

What can we gather from this? First thing we notice is that Serena is actually winning more points on serve than she was last year - on both first and second serve. She is serving significantly more aces this year – an extra 0.2 per game – but also more double faults. Combine these facts together and we can probably conclude that she is going all out on the serve. She is looking for big aces and unreturnable serves with the first serve and taking more risks on the second serve, resulting in winning more points quickly, but also in more double faults. It is interesting that, despite the increase in points won on her serve, she is still facing the same number of break points per game as she was in 2013. It would suggest that she is maybe enjoying more quick and comfortable service games, but this is being counteracted by having more service games where her opponent is getting chances. In other words, her service games are verging toward the two extremes.

However, it is the return game that would appear to have declined this year. The points won on return has dropped by 3.0%, which is a significant margin, although again, it has only resulted in a small drop in the break points created per game, which has fallen by just 0.02. Again, this may suggest that she is still getting break point opportunities, but that she is also giving her opponent more easy holds during the match.

Her two break point rates* have also dropped significantly in 2014. The conversion rate of 112.6 in 2013 was an exceedingly high value – previously in her career, this value has tended to be between 100 and 103, where it has returned in 2014. The save rate of 92.5 in 2014 is slightly low, but in the past, she has managed to overcome a low save rate by the rest of her game being at such a high level.

So, how do those figures convert to actual games won? The table below gives an indication:

Statistic	2014	2013
% of Service Games Won	81.8%	84.3%
% of Return Games Won	42.0%	50.3%

Despite winning more points behind both her first and second serve, Serena has actually held serve less often in 2014 than she did in 2013. The bigger change, though, is in the return game. Last year, she was winning over half of her return games. However, this year, this figure has dropped by 8.3%, which is a far bigger change than the earlier stats might have suggested.

From what we have learned so far, we might draw the conclusion that Serena’s actual serve itself is working as well as it has ever done, but that her ground game is beginning to decline. Whether this is because her speed around the court is slowing slightly, meaning that she is unable to get into position, or whether it is simply age slowing her reactions, we cannot tell, but this would seem to be indicated by the stats.

We can dig further into this to try and find further evidence to support our theory. Here are some further statistics to look at:

Statistic	2014	2013
% Non-Ace 1st Serve Points Won	67.7%	70.2%
% Non-DF 2nd Serve Points Won	60.2%	56.1%

I have used the first of those statistics – the % Non-Ace 1^st Serve Points Won – as a proxy for looking at how players perform in rallies. We can see that on points where Serena gets her first serve into play, but does not serve an ace, she is winning 2.5% fewer points than she was in 2013. Interestingly though, she is actually winning more of the points on her second serve when she does not serve a double fault. This ties in with our idea earlier that she might be going for it more on the second serve to try to shorten points and avoid getting into rallies.

I now want to look in more detail at those break point numbers from earlier. If you recall, Serena’s break points created dropped from 0.90 to 0.88 per game, while the break points faced on her own serve remained constant at 0.46. This seems slightly out with the game win percentages that we saw, so could do with some further investigation.

Before looking at the statistics, my theory was that she was creating almost the same number of break points, but that many of these were coming in the same games, hence the lower conversion rate. It may show in the basic statistics as the same number of break points created, but this is a less desirable way of achieving that.

As an example, let us imagine that two players both have break point figures of 2/12 in a match. The first player created six break points in one return game and six in a second return game. The second player created one break point opportunity in twelve different service games. From this, you would probably suggest that the second player had demonstrated the better return game as he had created opportunity in virtually every service game. The first player had created plenty of chances, but all in one or two service games.

So, does this pan out for Serena Williams in 2014? The table below shows the figures:

Statistics	2014	2013
% of Service Games with BP Faced	29.5%	28.8%
% of Return Games with BP Created	52.9%	56.9%

We can see here that Serena is having to defend break points in 0.7% more of her service games and that she is creating break points in 4.0% fewer of her return games. So, combining several of these figures together, Serena is creating break points in fewer return games and is converting those break points less regularly. These are combining to give us the 8.3% fall in return games that she is winning in 2014.

It also helps to shows us where the fall in service holds is coming from. Despite winning more points, she is facing break points in more service games than she was before and is saving those break points less regularly. She may win plenty of cheap service games, but she is struggling to win those games where her opponent is forcing her into rallies.

These struggles on return also seem to emphasis themselves on those occasions when Serena falls behind in sets. The excellent Dan Weston of TennisRatings has looked at this recently – in 2013, Serena was able to recover a break deficit and get back on serve a massive 75.6% of the time. However, in 2014, this has dropped remarkably to just 57.5% - still top 5 in the WTA, but a decline of 18.1% nonetheless.

In conclusion, there is plenty of evidence to suggest a reasonable decline in Serena William’s performance in the past twelve months. To be clear, she is still comfortably the best player in women’s tennis – her advantage over the rest meant that she could decline yet remain the best. However, compared to her previous level, this year has been a worry. She is being forced to go for quick finishes on her serve to compensate for a declining ground game, which is working to an extent, but means that when her serve is not working at 100%, she becomes beatable. Her overall ground game is causing a decline in her ability to create break points and to recover deficits.

As a final overall statistic to show that Serena’s dominance is decline, in 2013, she won 67.6% of all the games in the 47 hard court matches that she played. In 2014, this had fallen to 61.9% in her 42 matches. A fall of 5.7% in the total games that she has won suggests that her matches are becoming closer and she is becoming more beatable.


* The BP Conversion Rate is calculated by dividing the % of break points won by the player's % won on return to determine whether he performs better or worse compared to an average point when he creates a break point on his opponent's serve. A value of 100 corresponds to performing exactly the same, whether it is break point or not, a value greater than 100 corresponds to performing better on break point than an average point and a value lower than 100 corresponds to under-performing on break point. In the same way, the BP Save Rate divides the % of break points saved on a player's serve by the % of points won on serve to determine whether he performs better when facing break point.