Last week, I was at the ballpark watching my Phavorite baseball team lose in extra innings. In the bottom of the tenth, my team had the bases loaded with two outs. I noticed that next batter was in the on-deck circle. The question in my mind is why. The current batter will either end the game by getting on base or the game will go to the 11th inning. There is no way the on-deck batter will bat in the current inning, so why bother warming up? He wasn't just standing there either. He was swinging the bat with the donut and stretching, etc. Is there a rule that the on-deck circle must be occupied even in the situation I just described?