prop bet
n.— «If placing a bet on either team or the over/under is just not enough to satiate your gambling jones, there are numerous other ways to find action—these wagers are called “prop bets.” Do you have enough confidence in the Cardinals to wager on them without taking the 7 points? Then play them straight-up and make more than 2-1 on your money. Does your gut tell you that Troy Polamalu will intercept a Kurt Warner pass? You can wager on that, too.» —“Super Bowl 43: Prop betting sheet” Sporting News Jan. 28, 2009. (source: Double-Tongued Dictionary)
Further reading
The expression to go chalk has to do with rankings in an athletic tournament and harks back to when seeded teams or players were listed on a chalkboard. To pick chalk means to choose one’s favorite competitor, and you can also speak of a chalk...
A retired astronomer in Tucson, Arizona, is curious about the expression What are the odds? The idea of odds meaning “the likelihood of something occurring,” goes back to the idea of odds and evens and something odd being the thing that’s different...
short for “proposition”…
http://en.wikipedia.org/wiki/Proposition_bet
More citations for “prop(osition) bet” here.