Whatever the legal definition of wagering is, my understanding is the same as lefty's: bowling is a game of skill, not a game of chance, so it's legal. Many leagues and houses have put an end to 50/50 raffles because it's considered gambling, so someone somewhere is looking at bowling with their no-gambling eye.
Now everyone here knows just how much skill and chance really is in bowling, but it's not considered a chance game the way something like poker or craps is.
SH