Answer:
Because if you don’t make a decision quickly, the players may see that as a sign of being unsure of yourself, and they will attempt to capitalize on that to get an advantage. In addition, if the decision being made is major (such as, for example, a targetting penalty in college football, or a penalty kick in soccer), any delay may cause emotions to bubble over and cause a conflict between the teams, since both teams may start arguing with each other instead of playing, and that’s how brawls/mass confrontations occur.
