Details about alleged assaults involving a group of teenagers at Whites Bay, near Rarangi, were played out in the Blenheim District Court on Wednesday.

Thomas Ewan Patterson, 19, of Blenheim, has denied assaulting a woman, assault and assault with intent to injure, which a Crown prosecutor says all happened after Patterson was "kicked in the nuts" and became angry.

The jury trial began on Wednesday and is expected to finish on Thursday.

Crown prosecutor Mark O'Donoghue said Patterson and a group of friends were at Whites Bay along with another group of teenagers on the night of February 26 last year. Most had been drinking.

Patterson and Courtney Stewart, a year 13 student, had been "play-fighting" when she accidentally kicked him in the testicles, he said. He lost his temper and chased after her when she ran away, pushing her in the back so she fell to the ground. He then stood over her with a closed fist.

Another teenager, Tom Knowles, pulled him away but was punched in the face. He ran away and Patterson chased him.

Mr O'Donoghue said another teenager, William Murray, tried to calm Patterson down, "but had the opposite effect". Patterson punched Mr Murray in the head and put him in a headlock which restricted his breathing, he said.

Mr Murray eye-gouged Patterson so he would let go and shortly afterwards Patterson ran and hid in nearby bushes and was later arrested by police.

Defence counsel Nikki Utting said Patterson denied hitting anyone and put Mr Murray in a headlock in self-defence because he had grabbed him in an aggressive manner. Patterson said Miss Stewart and a few other girls were spilling their drinks over him and his friends when he got angry and told them to leave. They were not play fighting, he said.

She returned a short while afterwards and kicked him, which made him to fall to the ground for 10 minutes.

When he got up, he chased after her and she stopped and turned around, at which point he ran into her and she fell over on the ground. "She [Miss Stewart] seriously assaulted me. I'm confused as to why I'm sitting here and not her," he said.

Defence witness Jacob Eden, who was a sober driver that night, said there was "nothing accidental" about the kick.

Miss Stewart was running towards Patterson "as if she was going to punt a football". She meant to hurt him, he said.