To anyone who doesn't know that's what's going on, it sounds like they're booing, and it probably takes little more to assume that they're booing him because his name is Muhammad. I certainly saw that popping up on blogs yesterday. Not having followed Da Bears that much, I wasn't aware of it either, but I figured that must have been what was happening, as I did not think the fans could be that crass and stupid. But I suspect that the worldwide audience expects American to be that crass and stupid. Cheryl says the announcers on her coverage didn't explain what was happening. I doubt many others were either.
Sigh. Americans cannot necessarily be proud of themselves for many of their actions, but this was not a racist act by Stupid American Football Fans.
Ironically, according to his Wikipedia entry (which can't necessarily be considered authoritative), he's apparently a Christian.