I was wondering when you can leave on a fly ball when tagging up. Is it when the fielder has complete control of the ball, or when they make contact with it. I asked an umpire one time and he said that the fielder must have complete control of the ball. I was thinking recently and I asked myself, couldn't the fielder bobble the ball and run in at the same time and then make the catch by the time they get to the infield? Just wondering...