When people play a game called "football," they often need to use something called "timeouts" to stop the game for a short period of time. This gives them a chance to talk to their coaches or come up with a plan for how to play the game.
However, the people who make the rules for football realized that some teams were using too many timeouts and slowing down the game too much. That's why they made a rule called the "McCallum rule" to limit the number of timeouts a team can take.
The McCallum rule says that each team in the game can only use three timeouts in each half of the game. This means that they have to be careful and choose when to use their timeouts wisely, so they don't waste them when they really need them later on.
Overall, the McCallum rule helps make the game of football go more smoothly and quickly, while still giving teams a fair chance to stop the game and plan their next steps.