[jTheUmp]

Originally Posted by BillyMac

My daughter played high school softball on a state championship team. Many games were played at a very high level. In one close game, the other team's top hitter led off, and fouled a ball, that had been used for a few innings, out of play. The umpire put a brand new ball, hard as a rock, into play, which the hitter fouled off behind our bleachers. We all looked at each other and decided not to retrieve it. By this time the other ball had been tossed back to the umpire, who put it in play. That "soft" ball was softly grounded to second base. Two outs later, we were up, and we found the "hard" ball.

Which is why the baseball and softball mechanics manuals say that you should replace the ball in play with a replacement ball at the start of the next half of an inning, if one of your replacement balls hasn't yet been used.