Ball Spin in Pro Tennis

By John Yandell

Part 2

In the first article on our study of spin rates using high speed cameras, we looked at the results for groundstrokes and the serve. This article adds the data on returns and the net game to complete our picture of the amazing spin rates we found in world class tennis.

We also take a look at another surprising factor in generating spin--the bounce of the ball on the court. Again, we found something amazing. The friction of the bounce more than doubled the amount of spin already on the ball in the air, and converted it to pure topspin after the bounce, or something very close.

Return of Serve

Although there were significant exceptions, our data showed that in general the top players hit their returns with less spin than their groundstrokes. During our filming we were able to record over 25 returns on the men's side and almost 40 on the women's. It makes sense that the returns would have less spin going out, because of the heavy spin on the incoming serve, particularly second serves. This spin had to be negated or reversed first, making generating out going spin more difficult than on incoming balls with less spin.

For some of the men, we found the spin rate was about the same as the forehand groundstroke. We filmed 4 Sampras forehand returns and found they were hit at similar spin rates to his regular forehand, averaging 1899rpm. But Andre Agassi and Michael Chang on the other hand recorded forehand returns that had half or less topspin compared to their groundstrokes.

Men's Forehand Return

Men's Forehand Returns versus Forehands

Men's Backhand Return

The decrease in spin on the return was more dramatic on the backhand, although this was possibly due to the larger data pool--17 backhand returns versus 10 for the forehand return. Four Pete Sampras backhands averaged 1899rpm, about 14% less than on the forehand. 5 backhand returns from Andre Agassi again showed a far more dramatic decline, averaging 992rpm, or 43% less spin than his backhand groundstroke.

Shot: Men's Backhand Returns versus Backhands

Spin on The Women's Returns

The tendency to hit with less spin on the return was more pronounced on the women's side. The women's data included more incidents than the men's: 21 forehand returns from 7 different players. With the exception of Martina Hingis who generated virtually the same amount of topspin on her forehand return as on her regular forehand, the other 6 players all showed substantial declines. Anna Kournikova for example, averaged 1038rpm on 8 forehand returns, versus 1713rpm for her forehand groundstroke. This equalled 37% less topspin.

Women's Forehand Return

Women's Forehand Return versus Forehand

On the backhand side for the women, the team collected the most return data, 18 incidents from 7 players. Martina Hingis again recorded virtually the same spin rate on her return as on her backhand groundstroke, 1108rpm on the return, as compared to 1147rpm on her groundstroke. The other players all showed significant drops. Venus Williams, for example, averaged 736rpm on the return, compared to 1429rpm or her backhand groundstroke, almost exactly half the topspin.

Women's Backhand Returns

Women's Backhand Return Verus Backhand

Underspin in the Women's Return Game

In addition to the returns hit with topspin, we also were able to record several women's returns hit with underspin. Jana Novotna hit 2 backhand returns that both registered underspin at 3000rpm, only slightly less than the underspin recorded on her slice backhand groundstroke. Two other slice returns also fell within the general spin range of the women's slice groundstroke.

Women's Slice Backhand Returns

In addition we recorded 2 forehand slice returns from Novotna, averaging slightly over 2000rpm. As with the slice groundstroke, the spin rate is probably due to the fact the ball approaching with topspin is returned spinning in essentially the same direction, requiring less racket head speed.

Women's Slice Forehand Returns

The Net Game

Capturing spin data on the net game in pro tennis proved to be the most difficult. Serve and volley play is relatively rare in modern tennis played on hardcourts, such as at the Open.

Following the players' movement and maintaining the necessary camera framing to count the spin rates was also a challenge for our team when the players did go to net. In addition, many exchanges at the net ended without a clean volley, either with a passing shot from the opponent, or a missed passing shot, or a volley errors. All these factors reduced the number of incidents which we were able to measure.

Although our data included far fewer incidents, we still recorded about 30 examples of spin on the various net shots in the game, although the data here must be considered more tentative than on the groundstrokes and the serves.

The Forehand Volley

In the data we found that the forehand volley appears to be one of the "flatest" shots in tennis, and hit with relatively similar amounts of underspin by both men and women. For example, 3 forehand volleys from 3 different players on the men's side ranged from 600-882rpm. Seven forehand volley's from 5 players on the women's side ranged from 718 to 1250rpm, the highest being a forehand volley recorded by Martina Hingis at 1250rpm. The average underspin for the men was 772rpm, versus 846rpm for the women.

Men's Forehand Underspin Volleys

Women's Forehand Underspin Volleys

In addition for the women's side we recorded 2 incidents of swinging forehand volleys, a shot once thought impossible, but pioneered in the pro game by Andre Agassi and now hit regularly by many players. Both swinging volleys were hit with substantial topspin, one by Anna Kournikova at 1500rpm, and the second by Martina Hingis at 2500rpm.

Women's Swinging Forehand Volleys (Topspin)

The Backhand Volley

On the backhand volley, both men and women appear to hit with more underspin than on the forehand. Three underspin backhand volleys on the women's side, including 2 from Hingis, ranged from 1071 to 2143rpm, averaging just over 1600rpm.

For the men, 8 backhand volleys from 4 players ranged from 1200 to 2586 rpm and averaged slightly more than 1927rpm. This included 4 from Pete Sampras which averaged 1884rpm.

Men's Backhand Underspin Volleys

Women's Backhand Underspin Volleys

The Overhead

On the overhead, we recorded 4 incidents for the women averaging over 1200rpm, 3 of which were hit by Hingis. A single Michael Chang overhead on the men's side registered 1000rpm. In general we may conclude that although pro players generate substantial spin at the net, it is less than on the groundstrokes and on the serve. This conclusion makes obvious sense because of the far more abbreviated swing patterns at the net, as well as the lower velocity on the volleys compared to the other shots, as recorded in our ball speed experiments.

Women's Overhead

Men's Overhead

The Drop Shot

Among the over 700 incidents of ball analyzed by the team were a half dozen drop shots and drop volleys. The results were consistent with the general perception that a key to the shot is the ability to hit with substantial underspin. The team recorded drop shots from Monica Seles, 2 backhands and a forehand, that averaged 2145rpm, substantially more spin than on her topspin groundstrokes that ranged from 1200 to 1300rpm.

On the men's side 5 drop shots form 4 different players ranged from a low of 1364rpm for a backhand drop volley from Tim Henman, to a high of 3000rpm on a Marcelo Rios backhand drop shot. The average was 2296rpm. The implication is that, as with the slice backhand, shots hit with underspin have similar spin rates in the men's and the women's games.

Women's Drop Shots (Underspin)

Men's Drop Shots (Underspin)

The Bounce on the Court

One of the major sources of the heavy spin generated in pro tennis is actually completely unrelated to the players. This is the bounce of the ball on the court. This collision lasts only about 1/250 of a second, but radically alters the speed, direction, and spin on the tennis ball.

During the Open filming we were able to record over 60 incidents in which it was possible to measure the spin before the bounce and after the bounce, as well as the spin on the players hit that followed. The results showed how in general, the bounce added significant additional topspin to the flight of the shot.

In the case of balls that approached the bounce with topspin, the results were quite similar for both the men and the women. In both cases the bounce added over 2000rpm of topspin to the shot. This included balls hit to players including Pete Sampras, Andre Agassi, Michael Chang, Venus Williams, Anna Kournikova, and Martina Hingis. For the men, 31 incidents averaged 1324rpm before the bounce, and 3355rpm after the bounce and before the hit. For the women, 21 incidents had an average spin of 995rpm before the bounce and 3129rpm after the bounce.

The data also showed that on average, the amount of spin on the ball after the bounce was actually much greater than that generated by the players themselves. We noted above that only Sergi Bruguera's forehand was hit with topspin in excess of 3000rpm, with the majority of players hitting far less average spin.

Our ball bounce data showed that, for the men, the average spin rate of 3355rpm after the bounce and before the hit was slightly faster than Bruguera's average forehand. Although the players were hitting a ball spinning over 3000rpm after the bounce, the actual spin they generated on their own outgoing shots was on average less than half than the oncoming spin, an average of 1619rpm. For the women, the ball after the bounce was spinning at an average rate 3129rpm before the hit. The average spin the women players generated after hitting this ball an average of 1128rpm.

Men: Oncoming Balls Spin Rates Before Bounce

Average Spin Gained After Bounce: 2031
Average Spin Lost After Hit: 736

Women: Oncoming Balls Spin Rates Before Bounce

Average Spin Gained After Bounce: 2134

The results of this breakthrough study gave us a critical base in understanding the role of spin in the mysteries of the heavy ball. Inevitably, this work led to a new set of questions.

If this study represented the total spin rates in pro tennis, and could be loosely categorized as "topspin" and "underspin" what were the actual spin components in the pro ball. It was apparent from visually examining the footage that many "topspin" groundstrokes had significant sidespin components. What were the exact interrelationships there? Similarly, it appeared there was no such thing as a pure "slice" serve or a pure "topspin" serve. All the pros serves seemed to be spinning with some combination of the two. But again, what combination?

The second major question had to do with the interrelationship between our first two studies. How did ball speed and spin mix and interact in the pro game? Did more speed always mean less spin? What effect did various combinations of speed and spin have on the so-called "heaviness" of the ball?

These questions required new more complex filming protocols and new methods of analysis. Stay tuned to see what happened when we set out to devise them and address our additional questions.