Sure, you *might* not need it for *every* game, but you never know when a 300 lb linebacker is gonna put his shoulder into your junk either. The only difference is that when you're on a bike, you're more likely to die, that's all.

I live out in the Michigan countryside, and I've spoken to a number of guys who don't always wear helmets (even though it was mandatory, until a week or two ago) and I asked them why. They usually say 'Oh, because there's nothing around'. And they're right, there's not usually any cars. But about the time you hit a squirrel (or worse yet, a deer - "in Michigan there were 63,136 car-deer crashes on record for 2002") or even a piece of glass that blows out your tire..
I ride a cruiser, and I've got a full-face 'sporty' looking helmet because I do a lot of night riding. Trucks and tractors out here throw stones like confetti at a parade, and a June Bug ain't too pleasant to get up close and personal with at 70 MPH either.