Police say they have identified a man who ran on to the pitch at last night's Sheffield Wednesday v Leeds United derby football match and struck a goalkeeper.
Sheffield Wednesday's Chris Kirkland was attacked by the Leeds United fan during last night's game at Hillsborough.
Within minutes of the slap football fans swamped social networking sites vowing to identify the man.
TiG and the Gloucestershire Echo understand the man police are looking for is Aaron Cawley from Hester's Way.
A spokesman for South Yorkshire police said: "With the public's assistance we have clearly identified the offender who ran onto the pitch during last night's game between Sheffield Wednesday FC and Leeds United FC and who is suspected of assaulting the Sheffield Wednesday goalkeeper
"We are dealing with a complaint made by the player and we are currently taking statements, collating evidence and making inquiries to locate and arrest the offender.
"We are also using CCTV footage from around the ground to identify the suspect who may have been responsible for offences before, during or after the match.
"I would like to thank the supporters and general public who have provided information and assisted with our inquiries."
Inspector Joseph Tierney, of Gloucestershire police, said: "A suspect has been widely identified online in connection to the incident at Hillsborough and that is the line of inquiry we are actively pursuing at the moment.
"No arrest has been made so far but we are cooperating with South Yorkshire police who are leading the investigation into the incident."
The incident happened shortly after Kirkland conceded an equaliser at Wednesday's Hillsborough Stadium. The game finished 1:1.
The man was one of a number of Leeds' fans who ran on to the pitch in celebration. He slapped Kirkland in the face with both hands, knocking him to the floor. The match, which was televised live on Sky Sports, finished 1-1.
Former England keeper Kirkland said in a statement released by Wednesday today: "I was gutted with conceding the goal and had my head down as I kicked the ball down the field so we could restart the game.
"I was looking at the ground but when I looked up, I caught a glimpse of someone coming towards me on the pitch.
"I thought he was going to give me some abuse but then suddenly he came at me with both hands and I was stunned.
"I felt the full force and I was just shocked because you never know what could have been in his hands."
Leeds issued a statement after the game pledging to hunt down the man involved in the incident.
It read: "Leeds United Football Club would like to publicly apologise and condemn the action of the fan who came on the pitch and attacked Sheffield Wednesday goalkeeper Chris Kirkland. The club will fully co-operate with the police and the football authorities in identifying the individual concerned.
"After the week football has endured there is no place for this type of behaviour and the majority of Leeds supporters will be ashamed of his actions."
A large number of the Leeds fans housed in the Leppings Lane End sang about child abuse charges dropped against Wednesday manager Dave Jones.
The Wednesday fans also stoked things up with songs about two Leeds fans killed in Turkey in April 2000. Leeds supporters responded by throwing bottles onto the field and clashing with police.
Jones called for Leeds fans to be banned from "every away ground".
He went on: "You talk about racism, the chanting, that's a form of racism. And then (for the Leeds players) to go and wave at them... not in my book. You don't wave at them after that.
"I thought it had gone out of our game. The authorities have to look at it and sort it. I'm talking about an incident when we should be talking about the football. We're talking about vile animals. That's what they are. We talk about racism, but that, we need to sort that."
Anyone with information is asked to call police on 101 or Crimestoppers on 0800 555 111.
