UNIONDALE - Nassau police say they have arrested a teen for trespassing at Uniondale High School and allegedly assaulting a security officer.

Investigators say 17-year-old Kevin Allen had been expelled from the school and was prohibited from returning to the campus. On Monday, they say he showed up, and a 79-year-old security officer repeatedly asked him to leave.

Police say Allen refused, then struck the officer in the back of the head and pushed him to the ground. The officer was hospitalized to be treated for neck and leg pain.

Investigators say they tracked Allen down and charged him with assault, criminal trespass and burglary.

It is unclear why Allen was expelled from the school.