The QPR fan ran onto the Loftus Road pitch to remonstrate with Birmingham City supporters in the away end after missiles - including coins - were thrown.
Video footage then shows the man being punched to the ground after a confrontation with an away supporter.
The clash was among a number of incidents that happened during the Championship game at the weekend which led to three arrests and a police investigation.
Footage, which has gone viral on social media, shows the angry QPR fan react after missiles are hurled towards disabled supporters.
The man, wearing a green jacket, confronts a Birmingham fan in blue.
The QPR supporter is floored near the pitch by a single blow to the face to cheers from the away stand.
Stewards then step in to intervene and drag the injured man away as away supporters chant.
A fan was punched to the floor after confronting supporters for throwing missiles at disabled fans
Extra security and police were then deployed between the home and rival supporters.
Several incidents broke out during the game on Saturday, resulting in a number of fans needing medical treatment.
Metropolitan Police officers resorted to using batons to keep fans in check and were subject to attacks by fans.
Three men were arrested during the heated match - one for invading the pitch, one for racially abusing a police officer and another for a public order offence.
Several incidents occurred during the heated match
The coin throwing incident is the fourth in the last few weeks involving missiles being hurled during games at English football grounds.
West Brom midfielder Chris Brunt was left with a cut eye after being hit by a coin thrown by his own fans.
One fan claiming to be a QPR supporter in the affected stand branded the Birmingham fans "absolute animals".
He posted on Twitter: "Pound coins whistling past my head. Not one officer by the Birmingham fans. They're a disgrace."
A spokesman for Metropolitan Police said: "A large number of Birmingham supporters caused a disturbance in Ellerslie Road near to Loftus Road Stadium.
"Cordons were put in place to assist police officers in ensuring public safety. In addition, officers used batons to restore order where the behaviour of supporters was violent and potentially dangerous. Two officers were injured.
The man confronted away fans for throwing coins
"A number of supporters also sustained injuries and were treated by police medics. We are not aware of anybody receiving hospital treatment.
"There was further disorder inside the stadium, including missiles being thrown from the away stand towards home supporters.
"A QPR player was also struck by a coin thrown from the away stand. Shortly after the match, a home supporter was assaulted in Ellerslie Road.
"The victim was treated by London Ambulance Service for a broken nose. There has been no arrest in relation to this incident.
"Officers will examine CCTV footage of disorder in and around the ground and, wherever possible, police will identify and arrest anybody suspected of committing criminal offences."
A spokesman for QPR said: "The club can confirm it is co-operating and assisting the police in their investigation in relation to the incident that took place when a QPR fan confronted a Birmingham City supporter in the first half of Saturday's fixture at Loftus Road.
"In addition, both the club and the police are currently reviewing CCTV footage regarding the coin throwing incident which came from the away end following QPR's second goal.
"The club deplores the behaviour of those involved in the incidents and will continue to cooperate with the police to ensure the correct sanctions are made.
"Once both investigations have been concluded, the club - in communication with Birmingham City - will deal with the matter internally."
The man was floored by a single blow
A statement on the Birmingham City website criticised the handling of the accusations by QPR and the police against their supporters.
The statement read: "Birmingham City Football Club reiterates its zero tolerance policy to anti-social behaviour by supporters.
"We note allegations of coin throwing arising from the match at QPR on Saturday and we stress that the club will take the strongest possible action in dealing with any individual found to have indulged in such a deplorable act.
"The club also wishes to express its extreme disappointment that statements were released to the media during and after the match by QPR and Metropolitan Police without consultation with Birmingham City FC or West Midlands Police.
"A number of issues have since been brought to our attention from Saturday's match in regard the stewarding and policing that are of concern to the Club and our supporters.
"We read from the Metropolitan Police's statement that three men were arrested, one for pitch encroachment. The QPR supporter who walked round pitchside to confront Birmingham City supporters was, we understand, not arrested."