Predicting Break Point Performance

Break points are some of the most important points in a tennis match. Whether for the server or the returner, winning those points is often the difference between winning and losing the match. This raises the question, are there players that perform better than others on these big points?

The most commonly quoted statistics in this area are % BP Saved and % BP Won. Earlier in the year, the ATP wrote about how Ivo Karlovic had the highest % BP Saved for the year, ahead of Tomas Berdych and Jo-Wilfried Tsonga. Now that we have virtually reached the end of the season, looking at the list, we see John Isner, Ivo Karlovic and Feliciano Lopez at the top of the pile. However, the truth is that the big servers are always going to top this list. They could be mentally weak and under-perform on the break points, but because of their big serves, they will save plenty of break points.

The same is true on the % BP Won. The top returners will always top this list, while the 'servebots' will always find themselves at the bottom. Looking at the list, we find John Isner and Ivo Karlovic at the bottom with Feliciano Lopez fourth from bottom.

However, let us look more closely at Ivo Karlovic and John Isner. On a standard return point in 2014, Ivo Karlovic has won 28.0%, but when he creates a break point opportunity, he has won 31.6%. In other words, he is more likely to win on break point than on a standard return point. John Isner wins 30.1% of return points in 2014, but on break point, he is winning just 24.4% of points. In other words, he is less likely to win on break point than on a standard return point.

They both show up at the bottom of the list in terms of the actual number of break points converted, but we might suggest that Karlovic is better on converting break points than John Isner is. We can divide the % of BP Won by the % of Return Points Won to create a new measure - BP Conversion Rate. We can do the same with % of BP Saved divided by the % of Service Points Won to create the BP Save Rate.

These new measures give us an idea of how players perform on the break points and whether they over-perform or under-perform compared to their own average level. To give an idea, here are the BP Conversion and BP Save Rates for the top 10 in the WTA rankings:

Player	2014 BP Conversion Rate	2014 BP Save Rate
Serena Williams	101.7	97.4
Maria Sharapova	104.8	95.3
Simona Halep	105.3	93.0
Petra Kvitova	94.8	97.6
Li Na	109.1	102.4
Agnieszka Radwanska	104.3	95.5
Eugenie Bouchard	103.0	98.3
Ana Ivanovic	101.5	96.1
Caroline Wozniacki	106.2	99.8
Angelique Kerber	97.9	103.5

As we can see, the BP Conversion rate tends to be above 100, while the BP Save rate is usually below 100. This makes sense given that the server is usually under more pressure on break point and that the returner is likely to go for it more. Overall, the average BP Conversion rate is 104.5 and the average BP Save rate is 96.4.

Based on those averages, we might suggest that Li Na, Caroline Wozniacki and Simona Halep are particularly good at converting break points, while Petra Kvitova, Angelique Kerber and Ana Ivanovic are relatively poor. Similarly, Angelique Kerber, Li Na and Caroline Wozniacki are all strong at saving break points, while Simona Halep, Maria Sharapova and Agnieszka Radwanska are all below average at saving break points this year.

How does this compare with last year? The table below shows the conversion and save rates for the same players in 2013:

Player	2013 BP Conversion Rate	2013 BP Save Rate
Serena Williams	105.1	96.8
Maria Sharapova	103.5	98.4
Simona Halep	111.2	91.6
Petra Kvitova	107.6	105.5
Li Na	109.5	101.4
Agnieszka Radwanska	103.6	99.3
Eugenie Bouchard	101.3	93.6
Ana Ivanovic	102.1	97.3
Caroline Wozniacki	106.8	100.9
Angelique Kerber	103.7	101.9

Simona Halep, Li Na and Petra Kvitova all show up well in conversion rates in 2013, while Eugenie Bouchard, Ana Ivanovic and Maria Sharapova all show up poorly. In terms of save rate, Petra Kvitova, Angelique Kerber and Li Na show up well, while Simona Halep, Eugenie Bouchard and Serena Williams show up poorly.

This raises the question of whether certain players are consistently good at saving or converting break points, while other players are poor on the big points. This would fit in well with the idea that mental strength on the big points is hugely important in becoming a top level tennis player. Let us look at a plot of the 2014 BP Conversion Rate against the 2013 BP Conversion Rate to see whether a value in 2013 can allow us to predict what is likely to happen in 2014:

The chart shows all the players in the top 100 of the WTA rankings who have played at least 10 matches in both 2013 and 2014. At first glances, everything seems to look pretty random. In total, there were 14 players with BP Conversion Rates of over 110 in 2013. In 2014, just three of these players had values of over 110 - Yanina Wickmayer, Shuai Zhang and Francesca Schiavone. A further three of these players had values between the WTA average of 104.5 and 110, while three more players showed values of below 100.

If we look at the reverse, there were 19 players that had BP Conversion Rates of below 100 in 2013. None of these players flipped to a value of over 110 in 2014, but eight of them improved to values of above the WTA average in 2014. Seven of them remained below 100 in 2014.

The R squared value for this is 0.0032, which suggests that as a sample, there is virtually no correlation between the value in 2013 and the value in 2014.

Now, let us look at the same chart, but for the BP Save Rate:

There are 15 players with a BP Save Rate in 2013 that was above 102.0. Moving forward to 2014, there are four of these players that still have a BP Save Rate of above 100, while seven have dropped to below the WTA average of 96.4. Those four players that have remained above 100 in the second year are Barbora Zahlavova Strycova, Mirjana Lucic-Baroni, Elena Vesnina and Roberta Vinci.

As with the conversion rate, we find an R squared value of 0.0021, so again there is no overall correlation at all.

For those four players that we found with successive high values on the BP Save rate, let us look further back. The table below shows the values:

Player	2014	2013	2012	2011	2010
Barbora Zahlavova Strycova	102.1	108.2	103.8	99.4	102.7
Mirjana Lucic-Baroni	105.5	105.2	90.8	96.5	94.1
Elena Vesnina	100.9	104.1	92.7	94.1	93.2
Roberta Vinci	101.1	103.0	97.6	97.9	102.5

Barbora Zahlavova Strycova's figures are massively impressive. Four out of five years, she has finished with a value above 100.0, while the other year, she is still well above the WTA average. Mirjana Lucic-Baroni has scored above 100.0 for the past two years, but the three years before that, she was below average. Elena Vesina is pretty much the same as Lucic-Baroni in terms of three below average years before her recent improvement, while Roberta Vinci has three values of over 100.0 with two further above average values.

We cannot completely rule out certain players being particularly good at break points or certain players being particularly bad without further investigation, but on the whole, we cannot use the previous year's performance to determine how a player is likely to perform in the coming year on break points.