the game of throwing small objects, such as little balls of paper, inside a girls shirt with the goal of getting it to go in between her boobs.
Bryan: Look at Jessica over there. I'm going to play cleavageball! I'm gonna throw this paper ball inside her shirt.
Barney: You are going to miss! She doesn't have anything!
An eclectic sport where opponents try to make baskets by throwing small round objects into another player's plunging cleavage. Usually played with women.
Hilary scored a 320 in cleavageball last night, using Erica's double D rack.