Ulster rugby fans watched in stunned disbelief yesterday as Toulouse lock Trevor Brennan waded in amongst them in the stand and repeatedly punched a visiting supporter.
The amazing incident in the French city - reminiscent of footballer Eric Cantona's notorious kung-fu kick on a fan in 1995 - sent shockwaves through Ulster rugby last night.
Things weren't any better on the pitch. Ulster coach Mark McCall said Brennan, from Dublin, would be cited for striking Ulster lock Justin Harrison. Both players were sin-binned during Ulster's fractious 28-13 defeat by Toulouse yesterday, but McCall insisted Brennan should have been given a straight red card.
But it could be his clash with Ulster fans on the terraces - before he came on to the pitch - that could leave Brennan in serious trouble.
There were unconfirmed reports last night that Brennan, an ex-milkman and one of the most fiery characters in the world of rugby, had been arrested.
One Ulster fan, who did not wish to be named, claimed a young fan sitting two seats away from him - understood to be Patrick Bamford, a London- based Ulster supporter - was assaulted by Brennan.
"Brennan was warming up just yards away from us and the crowd were giving him some banter," he said.
"This guy, who was in his early 20s, was sitting beside my wife, just two seats away from me.
"He was shouting, 'Brennan your pub's crap. I had the worst night of my life there last night'.
"Brennan owns a pub in Toulouse. He seemed to be taking the banter in good spirits, he was smiling.
"Then he made his way through the crowd to this young fella. I thought he was going to talk to him.
"But he started punching him in the face and head, proper upper-cuts. He hit him at least three times, maybe four or five."
The fan described how the stunned crowd didn't know what to do.
"We were all so shocked, it was terrible," he said. "This guy had a black eye, his lips were cut and there was a lot of blood.
"Security came over and I told them this young man, who was with a group of friends, had just been assaulted.
"Then some medical staff from the Toulouse team came over to check him out.
"The next thing we knew Brennan was on the pitch playing.
"I've never seen anything like this in rugby."
The former Ireland and Leinster flanker soon found trouble on the pitch, too, when he traded punches with Ulster's Australian lock Justin Harrison, earning them 10 minutes in the sin bin.
Speaking after the match, Ulster star Paddy Wallace said: "The players on the pitch were not aware exactly what was happening.
"We knew some sort of incident had occurred but we continued on with the match."
David Gillespie, a committee member of the Ulster Rugby Supporters Club, said he couldn't believe what he was watching.
"It was an absolute disgrace. I have never seen anything like it happen at a rugby match.
"If Brennan is not cited for this outrageous behaviour, we will want to know why."
Edmund Curran, the Belfast Telegraph's editor-in-chief, was a spectator at the match. He said: "It was unbelievable. The scenes were quite extraordinary.
"When Brennan came on as a substitute, many people in the crowd stood and booed and shouted for the referee to take him off."
Last night, an Ulster Rugby spokesperson said it will be submitting a formal report to Heineken Cup organisers ERC on the incident.
In October last year, Brennan - an occasional rugby columnist with the Irish Times - was one of three Toulouse players cited after their 30-3 defeat by Ulster.