One of South Korea's richest men told a court he punched bar workers after his son was hurt in a scuffle, but denied using a steel pipe and stun gun.
Victims allege Kim Seung-youn hit them with an iron bar
Tycoon Kim Seung-youn, chairman of the Hanwha group, was arrested in May after being quizzed in the capital Seoul.
Mr Kim, charged with illegal detainment and assault with objects, said he beat bar workers, but that his bodyguards only joined later, when he "got tired".
Prosecutors say it was a revenge attack after a bar incident involving his son.
In March his son Dong-won, 22, a Yale University student, was reported to have needed stitches for an eye injury sustained in an incident in a Seoul karaoke club.
Mr Kim was appearing in the Seoul Central District Court for his first trial heaing.
Victims claimed they had been kicked, punched and attacked with a steel pipe and stun gun by one of South Korea's richest men.
They also say they had been forcibly taken to be attacked at a construction site in a mountainous area near the capital.
At one point Mr Kim told the court he lightly hit one of the workers on the head with a steel pipe to scare them, but later retracted the statement, and denied using a stun gun.
Kim's lawyers claimed the attack was not organised or premeditated and called for leniency for the tycoon, after saying that his prolonged absence from management could cause a crisis at the Hanwha conglomerate.
If convicted, Kim could face at least three years in prison, but the judge does have leeway to hand out a lesser sentence if there are mitigating factors.