How Fast Do Pros Really Hit?
At the US Open this year, Ben Shelton made headlines for hitting 149 MPH on his first serve two times (!) in the same service game. Pretty insane stuff, but there’s a catch. In the pros, shot velocity is measured as the exit speed from the racquet. As a ball travels through the air, air resistance slows it down by an average of 0.7% per foot (the direction of spin on the ball can affect this number). The ball then loses about 20% of its velocity when it hits the ground and continues to slow down to due to air resistance once again. The end result is that players on the receiving end return a shot that is (in the case of a serve) 55% slower than the recorded velocity. When Shelton’s serve flew by his opponent, the ball was moving about 70 MPH (still fast).
However, the average velocity of his serve was quite high - about 110 MPH over the length of the court. Taking everything into account, Shelton’s serve allowed his opponent about .48 seconds to react, move, and execute the return. For reference, closing one’s eyes for .4 seconds is considered blinking.
Returning a pro serve is as hard as one would think. During an average male pro serve, the ball moves about 120 MPH at contact and 58 MPH at the returner. This gives a returner about .7 seconds to react to and then hit a ball that could be 10-12 feet away from their position. An average tennis player has almost no chance against a pro serve, so how do the pros do it so regularly? Obviously, great reflexes play a part. But at those speeds intuition is the key.
Professional tennis players are masterful at reading the game. The slightest variance in a server’s racquet or toss can give away the location of the serve. For instance, if the toss goes left, the serve usually goes right. Beyond that, pros also have a knack for spotting patterns in their opponents such as where they like to serve in pressured moments or which side they’re likely to target for a weaker return.
Why do professional tennis organizations record shot speeds (this way)?
Recording shot speeds is interesting, and doing so by exit velocity makes tennis more sensational. For promotional purposes, the sport is better off if most spectators are awestruck by the speed and physicality of the world’s top players. The practice is also defensible if one believes that the difficulty of the shot should be reflected in the way that it’s measured.
However, one potential hazard arises when players compare themselves to the pros but use different recording equipment. There is a big difference between average velocity and exit velocity. Take the example of Swingvision, a popular consumer product that records players’ shots and analytics, including shot velocity. Those that don’t know better will be discouraged to see their serves and shots much slower than they would have thought. This is because Swingvision calculates average velocity from contact to bounce - and not super accurately. If the same practice applied to the pros, we’d see first serves averaging about 100 MPH, not 120. Shelton’s 149 MPH serve? That would have registered at 124 - still pretty ridiculous.
And what about groundstrokes? The commonly cited “average” is 75 mph, but again, that’s exit speed from the racquet. Using the Swingvision method, professional groundstrokes would clock in around 59 MPH.
