Roger Federer, who has long opposed the Hawk-Eye replay system and for the first few years of its use rarely challenged calls, discusses his current theory on using them.
“You get lucky and unlucky,” Federer said. “Sometimes you get tough calls from linesmen maybe on the other side of the court. You just go with your feeling. Sometimes it’s also the way the opponent then plays the shot, what’s the score. Sometimes you just get unlucky, especially if you get burnt early or lured into those challenges early in the set, you start losing them. I don’t want to say you lose your confidence, but you can’t challenge as much. The winning/losing ratio on the challenges isn’t important.
"At the end of sets, some players just burn them because you can’t carry them over in the next set. I don’t think I’m that good on the challenges. When you’re in the lead, you usually only challenge when you’re sure. When you’re down, you challenge because you have to.”