The Football Association is investigating the crowd trouble at the Championship match between Sheffield Wednesday and Leeds on Friday night which saw home keeper Chris Kirkland attacked by a fan.
A number of Leeds supporters ran on to the pitch after Michael Tonge equalised in the 1-1 draw at Hillsborough and one man confronted Kirkland before shoving him in the face with both hands, knocking him to the floor.
An FA spokesman told Press Association Sport: "We are investigating the events of last night and awaiting the referee's report."
The spokesman went on to say: "The FA condemns the scenes at Hillsborough last night. We have begun an immediate investigation and have been in contact with both clubs.
"We would call for the authorities to identify and bring before the courts anyone who was involved in any form of criminal disorder."
Kirkland required medical treatment before he could continue and police are working to identify the man.
Chief Superintendent Jason Harwin, of South Yorkshire Police, said a senior investigating officer would be working with a team of officers to identify those responsible for the disruption.
He said there had been five arrests for various offences including public order before and after the game, while three people were ejected from the ground and 12 were subject to dispersal orders.
In a statement released late on Friday night, he added: "First I would like to thank members of the public who have contacted us with information to help in the ongoing investigations following the incidents at Hillsborough tonight.
"Fans have now left the city and there has been no further reported incidents of violence and disorder."