British police have vowed to work with both Leeds United and Sheffield Wednesday to find the supporter who attacked goalkeeper Chris Kirkland in a derby match between the two northern English clubs.
The Sheffield Wednesday player was assaulted by a Leeds fan who invaded the pitch during a stormy 1-1 English Championship draw at Hillsborough on Friday, but was not caught by stewards.
The incident was one of a number of unsavoury ones to have occurred on a shameful night, which saw Leeds fans sing songs about criminal charges against Wednesday manager Dave Jones which were dropped in2000, while they also appeared to herald former broadcaster Jimmy Savile, who is currently the subject of a child abuse investigation.
Bottles were also thrown onto the pitch from the away end, while home fans sang songs relating to the deaths of two Leeds fans in Turkey in April 2000.
After the match, Jones branded the Leeds fans as "vile animals" and called for them to be banned from every away ground in the country.
South Yorkshire Police's chief superintendent Jason Harwin said: "During tonight's match, Sheffield Wednesday versus Leeds United, at Hillsborough incidents occurred where it is believed seats and bottles were thrown inside the ground.
"We are also aware of an incident whereby the Sheffield Wednesday goalkeeper has been assaulted by an individual who ran onto the pitch."
Harwin added: "Such incidents are not acceptable and won't be tolerated. We will be working with both clubs to identify and quickly bring to justice the persons responsible.
"Thankfully, such incidents are a rarity and we see a minority spoil it for the majority of genuine supporters."
The incident involving Kirkland occurred just after he had been beaten by a superb 77th-minute equaliser from Michael Tonge when Leeds supporters spilled onto the pitch in over-zealous celebration of the goal.
One of those fans ran up to Kirkland and, pushing both hands into his face, sent the stunned former Liverpool and England star crashing to the turf.
Police and stewards eventually cleared the field of the fans, but the visibly shaken Kirkland needed several minutes of treatment before he was able to continue.