Referee Mike Dean was hit on the forehead by what is believed to be a coin
A man has been arrested after the referee at the Cardiff City and Swansea City football derby was hit by a missile thrown from crowds at the game.
Mike Dean received a cut after he was hit on the head by what appeared to be a coin during the first half of the match at Cardiff's home ground.
His wound was treated and he carried on with the game with a plaster over his cut. The match finished 2-2.
A further five arrests were made outside Ninian Park for disorder.
Cardiff City chairman Peter Ridsdale said the man who threw the missile will be banned for life from any Cardiff City game.
He said the man was arrested after CCTV images were examined following the incident.
Mr Ridsdale said the incident made him "feel sick" and that he had apologised personally to Mr Dean, who is from the Wirral, Merseyside.
"It's a disgrace, it's unacceptable, makes you sick because obviously we spend a lot of time at Cardiff City trying to do the right things.
"Today was always going to be a high profile game. You don't expect idiots to do that and people like that have no place in football and certainly no place at Cardiff City football club."
He said they would be examining CCTV footage further to make sure just one person was involved in the incident as a number of coins appeared to be thrown at the same time.
But Mr Ridsdale insisted the club had done all it could to try to make the day as safe as possible.
"We've been working tirelessly with the police and Swansea City football club. There are more police here than any other football match," he said.
He said he hoped the club's "swift and decisive" action in dealing with the matter would show the football authorities that such behaviour would not be tolerated.
"There's always the problem that if one individual wants to get around the system they can do so but they will suffer the consequence," he added.
Witnesses said Mr Dean was hit by what looked like a coin while a player lay injured on the ground.
Cardiff manager Dave Jones said the incident overshadowed and soured a fantastic advert for Welsh football.
"It's sad because everyone will be talking about the man who threw the coin rather than a game which had everything - excitement, controversy and last minute penalty," he said.
Event commander Ch Supt Josh Jones confirmed a man had been arrested and police would be studying CCTV footage to identify others who were involved in throwing missiles onto the pitch.
"Five arrests have also been made outside the ground," he said.
"The post match investigation will aim to trace and arrest those individuals who became involved in incidents of disorder outside Ninian Park on Sunday.
"This process will be thorough and South Wales Police will not tolerate the type of behaviour displayed by a small but nevertheless significant minority of supporters.
"I would like to praise the majority of fans who heeded our advice prior to the match and contributed to the derby atmosphere.
"Anyone who was involved in disorder will be arrested and banned from attending future matches."
Police had previously warned supporters to behave at the key league match, which could be the last between the clubs at Ninian Park.
Hundreds of police officers were in the city to try to prevent crowd disturbances that have marred previous derby games.
The police operation, costing an estimated £250,000, included around 450 officers, horses and "spotters" looking for known troublemakers.
Officers escorted the 1,600 Swansea supporters, who were travelling in 33 coaches, into the stadium.
A total of around 35 arrests were made in two previous meetings - in the Carling Cup and the Championship - between the clubs this season at Swansea's Liberty Stadium.
Tensions were high at the game, which kicked off at 1100 BST, with both teams pushing for promotion to the Premier League.
Cardiff City will move to a new stadium next season but the two clubs could meet again this season depending on their final league positions.