Two people were stabbed at a youth gaelic football match in Co Tyrone on Thursday (July 6).
The attack, at Paddy Cullen Park in Cookstown, happened during a game between Cookstown Fr Rocks under-16s and Fintona Pearses under-16s.
A 42-year-old man has been released on bail following an arrest on Thursday night.
Ulster GAA Chief Executive Brian McAvoy told UTV: "I've been involved in the GAA for half a century or more and it's the first time I've ever come across an incident remotely like this.
"This is something that's totally alien to us, thankfully. It has never happened before and the wish is it never happens again."
SDLP MLA Patsy McGlone said: "It shouldn't be happening at any event anywhere, but this was an under-16 football match, a lot of kids here, a lot of young parents here and it really is your concern for those people that were here - the trauma associated with them and any risk or danger that they may have been placed in. Thankfully, that didn't happen."
In a statement, Tyrone GAA said they were taking the attack "most seriously".
It said: "Tyrone GAA are aware of an incident which occurred at one of our underage fixtures on the evening of Thursday 6 July. Tyrone GAA shall conduct our own investigation into the circumstances.
"As the organising body, we treat this incident most seriously, and will be offering our support to those affected. We can make no further comment at this time. Both clubs involved in the game said support was being provided to their young players and supporters."
Fintona Pearses GAC said their thoughts were with those impacted and "all focus is on the welfare of the children and young people present".
Cookstown Fr Rocks said: "The committee will now work to ensure that children and young people who witnessed this disturbing and very serious incident have the support and assistance that they require in the coming days."
Sinn Fein's vice president Michelle O'Neill described the attack as "shocking ".
In a tweet, she said: "My thoughts are with those injured and impacted. Anyone with any information should assist with police inquiries. "
She commended the work to assist and support the young people who were at the game.
SDLP MLA Justin McNulty, a former GAA all-Ireland championship winner, expressed shock.
He said: "The GAA is at the heart of so many communities the length and breadth of Ireland and people will be horrified at what has taken place here.
"Spectators, players and officials should be able to attend and participate in matches without being subjected to something like this..
"My thoughts are with the two men who were injured and I hope they make a quick and full recovery. I'm also concerned about the young players and spectators who will have witnessed this incident.
"I trust and know that the GAA locally will do everything they can to support those who've been impacted to help them to overcome what must have been a very frightening and traumatic experience."
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