A police doctor told a jury he suspected a teenager under arrest had been drinking or taking drugs.
Dr Simon Harris examined John Whelan the night he was arrested in December 1997 when he was aged 15.
Mr Whelan, now 22, is taking legal action against Sussex Police at Brighton County Court.
Mr Whelan, of Portland Road, Hove, is claiming compensation for assault, false imprisonment and malicious prosecution.
His allegations are denied by the police.
The jury heard Mr Whelan was arrested after youngsters started causing a late-night disturbance following a disco at St Richard's Community Centre in Egmont Road.
Mr Whelan claims he was heading home because he wanted to avoid any trouble when, without warning, a police officer hit him with a truncheon from behind on his buttocks before slamming him on to a car bonnet and handcuffing him so tightly he could not move his hands.
He was taken to Hove Police Station where officers lent on his back and legs as he lay face down on the floor of a cell while they searched him.
Dr Harris said he was called to examine the teenager for any injuries after a complaint was made he had been assaulted when he was arrested.
He said the teenager had acted in a calm and co-operative manner and had denied taking any drugs or drinking alcohol.
But, the doctor said, he noted during the examination he believed Mr Whelan had been intoxicated by drink or drugs because his pupils remained fully dilated when a bright light was shone at them.
The jury was shown a copy of the doctor's original notes which showed a question mark next to the comment that Mr Whelan may have been intoxicated by drugs or alcohol.
However, the doctor confirmed that no testing was carried out. The case continues.
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