In the Broncos locker room, he and a bunch of other o-lineman seemed to end up around the garbage can puking before the game. To me, his comment acknowledged that it was a completely normal part of what happened before the game. It happened every week. They probably would have preferred that it didn't happen (its a bit unpleasant) but they accepted it as a normal reaction to the pregame nerves, dealt with it, and moved on.

OPs son may be feeling as much anxiety about the fact that he's feeling this way as he is about the game itself. I think Eddie's comment about "normalizing" it is dead on. This is normal, this is OK, many people deal with this . . . now let's talk about learning some coping skills.

Maybe give him some mints and waterbottle pregame and tell him "hey, if you have to throw up, just do it. Let it fly!" Then he can rinse, suck on a mint and get ready for the game to start.