water polo

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A water sport in which two teams of swimmers try to throw a ball into the opponent's goal.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A water sport consisting of two teams of swimmers who have to throw the ball into the opponents goal.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a game played in a swimming pool by two teams of swimmers who try to throw an inflated ball into the opponents' goal