Q: Where do football players go before the big game? 
A: To the Toilet Bowl!

Explanation: If someone says, “I gotta go!” that person means, “I have to go to the bathroom.”  Imagine someone saying that while squeezing their legs together.  Football championship games are called bowl games, think The Super Bowl, The Rose Bowl, … The part of a toilet where one leaves waste is the toilet bowl, the part you see filled with water.  This joke is funny because it combines the ideas of going to the bathroom with a bowl game.  11 year olds might love this joke!