AMHERST, Mass. —  A tailgater skinny dipping inside a truck bed at a University of Massachusetts football game has been charged with assault for allegedly kneeing a campus police officer in the groin after being told to get out of the water.

Deputy Chief Patrick Archbald said 21-year-old Marshal D.P. Keating of Edgewater, N.J., was among several fans splashing around in the back of a pickup truck before Saturday's game against the University of Delaware.

When police told them to stop, Keating initially refused to get out. Archbald says he then approached the officer and kneed him twice in the groin.

The officer, whom Archbald did not name, was given morphine at a hospital. He could miss up to two weeks of work.

Keating is charged with assault and battery on a police officer, resisting arrest and disorderly conduct.