An 18-year-old man slid his watch over his knuckles and punched a 17-year-old student on the jaw.

The man was sentenced to eight months in a Young Offenders Institution at Croydon Youth Court on Thursday, February 23.

The man was one of four males who made an unprovoked assault on the teenager near the Charles Cryer Theatre, Carshalton in the evening of August 8, 2011.

Before the assault, they had been spraying people with water pistols in the Grove, Carshalton.

As they left the park, they taunted a group of young people saying: “Are you dry now?”

The teenager, who was one of the group, jokingly replied: “Next time you’re out with your water pistols, I’ll wear my swimming costume.”

The teenager was then attacked by the four males.

One of the men pulled his watch over his left hand knuckles and punched the him in the jaw.

As he struggled to defend himself, the other attackers punched him in the back of the head and whipped him with a belt on his back.

The injured man was taken to St Helier Hospital and kept in overnight for treatment suffering a black right eye and a deep cut to the right side of his jaw below his lip.

He had five stitches and suffered permanent scarring.

The 18-year-old man pleaded guilty to ABH and was sentenced to eight months in a Young Offenders Institution.