if anything, playing should keep your GPA up. i know at my school, anyone in sports had to maintain a B or C average (cant remember) and if you got one D, you were benched. If you failed anything, you were off the team. My graduating class football team was full of a bunch of smart mofos. They were a great team and execelled in school.

Football is great. I love it. If you like the game and are good at it, stay there. But if you're afraid of dropping grades or having no life, then quit. Quitters are losers though