The 420 Football League is an interesting concept. A bunch of stoners got together and made a sport out of smoking dope. You snap the ball by taking a toke, and you advance the ball one yard for each second that you can hold the hit. (source)
The NFL is not amused, and they sent a cease and desist letter to the 420 League. I’d say that the NFL probably has a decent dilution argument. On the other hand, the 420 league has a good parody defense. Of course, it would be a lot cheaper and easier to just change the logo.