What tennis pros look at when they pick a ball.

Before a tennis player makes a serve, they have to get in the zone. Novak Djokovic will bounce the ball first with his racket, then with his hand. Naomi Osaka will tap her thigh. Rafael Nadal will pull his shorts, the sleeve around his shoulders, touch his nose, and then finally move his hair to the back of his ears. But there's one ritual almost every player does. They're looking at the fluff. Choosing a tennis ball with the perfect level of fluffiness is a long-held tennis tradition, and some players believe the right ball can help them win. But does fluff actually make a difference? In a professional tennis match, six balls are used over nine games. Before serving, players typically ask the ball boy or girl for three or four balls and select one or two. And most of these players are looking for something specific. Try to get the ball that is more new for the first serve. Daniil Medvedev is a professional tennis player who's currently ranked number two in the world. He's defeated Novak Djokovic, Rafael Nadal, and Dominic Thiem. He just competed in the Ultimate Tennis Showdown and the French Open. And he cares about fluff. Try to find a ball that has less hair, actually, because it will go faster in there. You don't want this big ball, you know, that has a lot of humidity in it for the first serve because it's not going to go fast. Michael Costa, a former professional tennis player, does the same thing. I would always want the more compact, tighter felt ball for my first serve. I felt like that moved faster through the air. It gave me more confidence to hit that first serve. And I would save the kind of juicier, bigger, fluffier ball for my second serve as like almost a safety ball. I need this big, slow beach ball to get in the court in just in case I miss my first serve. Second serve, they're looking for control more than speed. My name is Patrick Moratogdou. I'm a professional tennis coach. I'm working with Serena Williams for the last almost 10 years. Yes, the Serena Williams. When the ball is fast, you have less control. So on the second serve, they don't want to hit a double fault. And the fluffier the ball, the more grip you have. It's kind of tactics. I should say it doesn't affect so much, like you're not going to win the match just because you chose a fluffier ball. So Ravi, how involved or how much information do you know about tennis? I think I know enough to be dangerous. And in terms of the science, I'm a pretty lousy tennis player. Dr. Rabindra Mehta works for the NASA Ames Research Center and has been studying the aerodynamics of sports balls for more than four decades. The fluff is the whole key. With tennis, you get what we call extra drag. Drag is the force that slows the ball down as it's flying through the air. Initially, when you pull it out of a can, you'll find it's pretty compact. And so it has one level of drag on it. But when you start playing with it, it tends to fluff up initially the first few games. And the drag actually goes up like the hair on our arms. It'll contribute to the drag. That's why swimmers have their own ritual of shaving all their body hair before big meets to make it easier for them to move through the water. To figure out how much the fluffiness of a ball actually affects its speed, Dr. Mehta and his team used a wind tunnel. We had the ball on a balance so we could measure how much drag force, how does it change. They compared tennis balls with different amounts of wear and proved that the fuzzier the ball, the slower it moves. And the way we proved that was to start literally shaving the ball to try and get it to match the other balls. And we were able to do that. On the court, this drag can mean that if a player serves with a fluffier ball, the person receiving gets slightly more time to react. And the server then gets slightly more time to return it. I was at the U.S. Open and we had some people there who were interested in what we were doing. And they actually sent us balls that had been used in the actual tournament. And so when we started looking at those balls, it was pretty obvious that they were preferentially using two or three balls out of the six. So it wasn't like there was equal wear. Beyond the science, the ball selection still serves a purpose. I believe when I'm match point down and I have to hit a second serve, that my rituals of finding that bigger, juicier, feltier ball are going to give me a tiny little bit of safety on the second serve. That little bit of confidence can be what helps you eke out the match. There is such an incredible amount of pressure and stress on them. So the fact that it makes them feel better, makes them play better. That's why routines are such a big part of the sport. The goal of the routine is to refocus for the next point and it becomes a habit. Some routines can be more obsessive than others, like Nadal meticulously lining up his water bottles on the sidelines. I don't think he even knows he's doing it anymore. He's done it for so long. But for many, that little ritual of picking the right ball is enough. Most of the players choose their balls. Serena doesn't, by the way. She's one of the only players who does not. She's taking only one ball to serve, one by one. So if she misses the first serve, then she asks for a second ball. But most of the players take two balls, keep one in their pockets. And she takes the first ball that comes. She never asks for another ball.