Former England goalkeeper Chris Kirkland was punched to the ground by a pitch invader amid violent scenes in a second-tier League Championship match between Sheffield on Wednesday and Leeds on Friday, bringing further shame at the end of a difficult week for English football.
Kirkland had just conceded a 77th-minute equalizer as Leeds came back to draw 1-1 in the Yorkshire derby at Hillsborough when a man ran onto the pitch from the Leeds supporters' end and struck the 31-year-old keeper in the face. Kirkland received treatment before continuing the match.
"I felt embarrassed to be a manager when I saw that. I thought it was an absolute disgrace," Leeds manager Neil Warnock said. "I think they should get the guy and prosecute him and put him in prison."
South Yorkshire Police said they were working with both clubs "to identify and quickly bring to justice the persons responsible."
Bottles were also thrown onto the pitch from the away end during the match, while Wednesday manager Dave Jones was taunted with songs about criminal charges against him which were dropped in 2000.
"They are vile animals," said Jones, who condemned Warnock and Leeds' players for applauding the away fans after the match.
"He's sore," Jones said of Kirkland. "If he'd have stayed down, I wonder what would have happened. I have an ill goalkeeper. They should be punished."
The fan returned to the stand after attacking Kirkland while trouble continued around him, with a number of other visiting supporters running on and off the field and stewards struggling to contain them.
Trouble had been brewing throughout the second-tier match, with a section of the Leeds fans clashing with stewards and police.
"Leeds United would like to publicly apologize and condemn the action of the fan who came on the pitch and attacked Sheffield Wednesday goalkeeper Chris Kirkland," Leeds said in a statement.
"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 behavior and the majority of Leeds supporters will be ashamed of his actions."
The incident came soon after England's Danny Rose complained of being racially abused by Serbian fans during an under-21 international on Tuesday.
Racism was already in the spotlight thanks to the year-long racism case involving John Terry, who on Thursday decided not to appeal against a four-match ban imposed on him by the Football Association for hurling a racial slur at an opponent during a Premier League game last October.