Here's what happened today - opponent hit a fast ball at me and I wasn't sure if the ball was gonna go out. I had very little time to react after the ball landed and hit the ball on the rise. I saw the ball was out. Could I have called the ball was out? I saw on TV that the pros do it all the time - they would hit the ball and after realizing that the ball was out before they hit it, they would immediately stop and challenge. It applies at the pros level. Does the same rule apply in USTA play? In case you're wondering, I decided not to call the ball out. My shot went to the net and I lost the game. I ended up winning the set but still I was wondering the whole time after that game.