Challenge, Anyone?

Roger Federer is getting teased, and not just because he lost the U.S. Open last week to Juan Martin del Potro. He is being mocked for his terrible eye. He challenged more calls in the U.S. Open than any other competitor, and yet he had one of the lowest success rates of any of the top players.

Insult to injury, right? Wrong. Federer is adept at challenging tennis calls, and he should challenge more of them — as should his rivals. Professional tennis players are almost certainly losing matches because of their unwillingness to do so.

Here’s how challenges work. Major tennis tournaments (like the U.S. Open) have multiple cameras arrayed around the court. This permits a simulated replay of a shot, showing to the millimeter where a ball landed on the court. So instead of futilely shouting, “You can’t be serious!” at linesmen and umpires, players can raise their hand immediately after a call and ask for a replay.

The rules allow three incorrect challenges per player per set. In a best-of-five-sets match (which is normal for men), that means at least 18 available challenges per match, none of which carry over from set to set.In other words, use ’em or lose ’em. A player can get an additional challenge if the match goes into a tiebreaker, or if a fifth set goes overtime.

Yet despite all these opportunities players have to dispute calls, at this year’s U.S. Open, men’s singles matches averaged 6.3 challenges that had a 29 percent success rate. Even Federer averaged a miserly one challenge per set in his 25 sets played at the Open. Why this reluctance to make a challenge? After all, the 29 percent success rate of challenges in the men’s singles matches shows that linesmen are regularly wrong.

And the rewards for challengers can be substantial. For example, the No. 10 seed at the Open, Fernando Verdasco of Spain, averaged 0.4 challenges per set and had a sparkling 43 percent success rate. If he challenged once per set, like Federer, and his challenge success rate fell to a similar 30 percent, it could mean one more point to him in a three-set match. If his success rate didn’t fall as much, however, and he challenged twice per set it might mean as many as three more points in a five-set match. Either way, it could be the difference between winning and losing.

It’s not all about math. There are also behavioral reasons that explain why tennis pros would shy away from challenges. Look at the sheepish faces on players when they’re wrong, and listen to the clucking from announcers. But players should worry about total challenges won.

Players also hang onto challenges “just in case,” only to have them expire when a set ends. But close line calls don’t always show up when you need them to.

So what should players do? Rather than fretting about Federer’s fondness for challenges, they should try to out-challenge him. Even challenge recreationally now and then. Sure, it might be embarrassing to challenge on a ball that looked well in, but who cares? The disruption to an opponent’s rhythm can be worth it, as can the opportunity to take a short breather after a tough rally. The real challenge is to ignore the giggling critics.

Paul Kedrosky, a senior fellow at the Kauffman Foundation, a center for economic research.