SALEM — An off-duty police officer who was hit by a water balloon Saturday night ended up arresting the alleged balloon thrower and the driver of the car she was riding in.

Off-duty Patrolman Ryan Davis was about to get on his motorcycle on Washington Street shortly before 11 p.m. Saturday when he was hit by a water balloon, according to a police report.

Davis looked up and saw a dark Nissan Pathfinder drive by and a woman's arm going back inside the front passenger's window, according to the police report.

A wet Davis got on his motorcycle and followed the sport utility vehicle around the downtown area, signaling for the driver to pull over.

The driver didn't pull over, but Davis did see the passengers in the rear seats laughing at him.

Davis reported he was able to pull up alongside the car and show his police identification, and he saw the driver mouth the words: "Oh (expletive), he's a cop!"

When the car stopped, Davis pulled the driver from the vehicle and placed him on the ground. He had the four passengers sit on the ground until Patrolman Fred Dubiel responded to Summer Street, the report states.

The driver, Christopher L. Lavoie, 17, of 33 Aborn St., Peabody, was charged with disorderly conduct. The front-seat passenger, Alexandra H. Parson, 22, of 44 Trask St., Beverly, was charged with assault and battery with a dangerous weapon (a water balloon) and disorderly conduct.

Inside the Nissan, police found a large bucket containing water balloons, according to the police report.