Zverev and Rublev Should Pick Up the Pace

There is a saying in tennis that you are only as good as your second serve. We can see the validity of that statement across all levels of the sport. Go to your local park, and you’re likely to see aggressive swings on the first serve, followed by a tentative tap on the second serve. At the highest level of the sport, the second serve becomes the battleground where the all-valuable breaks of serve get decided.

One component of an effective second serve is its velocity. All else being equal, a faster second serve will be more effective: it gets to the opponent faster, giving him/her less time to react, and hit a good return. Using data from the 2020 Nitto ATP Finals, I’d like to highlight a possible area of improvement for two of the young starts of our game: Alexander Zverev and Andrey Rublev.

Alexander Zverev is still only 23 years old, yet he has already been ranked as high as #3 in the world, and came tantalizingly close to winning his first Grand Slam title at the 2020 US Open. Andrey Rublev is also just 23 years old, and recently broke into the top ten of the ATP rankings for the first time. Both of them have (hopefully) more than a decade of high level tennis ahead of them, and plenty of time to add to their game. I would argue that being more aggressive on their second serves could help them close the gap on their competitors.

First, let’s look at how aggressive – in terms of comparing their second serve velocities to their first serve velocities – the two of them were at the 2020 Nitto ATP Finals. In each of the tables below, the first two columns highlight the average first serve and second serve velocities in their matches in London. The third column is just the average second serve velocity subtracted from the average first serve velocity. And the fourth column is the difference in km/h divided by the average first serve speed.

Let’s look at Alexander Zverev’ table for an example. In his group stage match against Diego Schwartzman, he hit his first serve with an average speed of 215.3 km/h, while hitting his second serve with an average speed of 150.1 km/h. That means, on average, Zverev’s second serve was about 30% slower than his first serve in that particular match.

Alexander Zverev

Andrey Rublev

Match	Average 1st Serve Speed (km/h)	Average 2nd Serve Speed (km/h)	Difference (km/h)	Difference (percentage)
Tsitsipas (Group)	197.0	144.4	52.6	26.70%
Thiem (Group)	198.4	147.1	51.3	25.86%
Nadal (Group)	192.4	150.5	41.9	21.78%

Two things immediately stand out. First of all, both Zverev and Rublev generate outstanding velocities on their first serves. For the three matches he played in London, Zverev was sitting (!) at around 210 km/h with his first serve. Yet both of them hit their second serves roughly 50 km/h slower than their first serves, with the lone exception being Rublev’s match against Nadal. In that particular match, part of the reason for the smaller difference was Rublev’s decrease in his average first serve velocity by about 5 km/h. Without looking at the data, I would guess that Rublev hit more slice first serves to target the Nadal backhand return in both deuce and ad sides of the court; the slice serve tends to be hit slower than the typical flat first serve.

Knowing that Rublev and Zverev lost in the ballpark of 25% of their velocity on their second serves in the majority of their matches, let’s compare them to the four players, who have made it out of the group stage in London.

Dominic Thiem

Match	Average 1st Serve Speed (km/h)	Average 2nd Serve Speed (km/h)	Difference (km/h)	Difference (percentage)
Tsitsipas (Group)	192.3	163.7	28.6	14.87%
Rublev (Group)	193.6	166.9	26.7	13.79%
Nadal (Group)	193.5	163.6	29.9	15.45%
Djokovic (SF)	195.0	162.3	32.7	16.77%
Medvedev (F)	195.1	161.7	33.4	17.12%

Rafael Nadal

Match	Average 1st Serve Speed (km/h)	Average 2nd Serve Speed (km/h)	Difference (km/h)	Difference (percentage)
Thiem (Group)	190.8	161.7	29.1	15.25%
Rublev (Group)	192.9	160.1	32.8	17.00%
Tsitsipas (Group)	192.1	162.4	29.7	15.46%
Medvedev (SF)	187.6	158.7	28.9	15.41%

Neither Nadal, nor Thiem, hit their first serves as fast as Zverev or Rublev did. Specifically, Zverev hit his first serve in London on average 20 km/h faster than Thiem. Yet Thiem averaged over 160 km/h on his second serve in all of his matches, while Zverev didn’t crack 160 km/h once. In terms of the percentage differential, neither Nadal nor Thiem have lost more than 18% of their velocity on their second serves in any of their matches, while Rublev and Zverev have never lost less than 20%.

It could be the case that Nadal and Thiem have just been extremely aggressive on their second serves. So how do Rublev and Zverev compare to the other two semifinalists: Novak Djokovic and Daniil Medvedev?

Novak Djokovic

Match	Average 1st Serve Speed (km/h)	Average 2nd Serve Speed (km/h)	Difference (km/h)	Difference (percentage)
Medvedev (Group)	196.2	157.5	38.7	19.72%
Schwartzman (Group)	193.7	162.4	31.3	16.16%
Zverev (Group)	195.4	156.8	38.6	19.75%
Thiem (SF)	193.6	145.0	48.6	25.10%

Daniil Medvedev

Match	Average 1st Serve Speed (km/h)	Average 2nd Serve Speed (km/h)	Difference (km/h)	Difference (percentage)
Schwartzman (Group)	199.1	160.8	38.3	19.24%
Zverev (Group)	196.4	157.4	39.0	19.86%
Djokovic (Group)	202.3	160.7	41.6	20.56%
Nadal (SF)	198.0	161.1	36.9	18.64%
Thiem (F)	200.5	158.3	42.2	21.05%

Looking at their respective tables, Djokovic and Medvedev were more conservative with their second serves than Nadal and Thiem. Medvedev hit his second serve fairly consistently about 20% slower than his first serve. For Djokovic, there is more variability in his second serve velocities, most likely due to tactical reasons. The important takeaway here is that Djokovic and Medvedev lost 25% of their velocity on their second serve in just 1 of their 9 combined matches in London . Zverev and Rublev lost more than 25% on their second serve in 4 of the 6 combined matches they played.

Maybe Zverev and Rublev don’t have to be as aggressive with their second serves as Nadal and Thiem have been. By the same token, losing 25% of velocity on one’s second serve, as compared to some of the other elite players, leaves something on the table.

A good first step might be to close that gap to the roughly 20% we have seen from Djokovic and Medvedev in London. In Zverev’s case, assuming his first serve averages 210 km/h, that translates to a 168 km/h second serve. For Rublev, assuming a 195 km/h first serve, that would be a 156 km/h second serve. Is that attainable, or too ambitious? That’s for Rublev, Zverev, and their respective coaching staffs to decide. But I would sure like to see them try to be as aggressive on their second serves as they are with the rest of their games.