The 30-year-old, who is a season ticket holder in the opposing team Nottingham Forest, was involved in storming the pitch after Nottingham won the double meeting on penalties. Once on the pitch, he headed Sharp so that the Sheffield United player fell over and needed to be stitched in the lip.
The man admitted in court that it was he who beheaded Sharp in what the prosecutor calls “an intentional and meaningless act of violence”.
Nottingham have said after the incident that the person who will be sentenced will be suspended from the team’s matches for life.
Billy Sharp played earlier in his career for Nottingham and writes on Twitter that “an idiot ruined an incredible football night” but adds that he has no grudge against other Nottingham supporters.
Nottingham face Huddersfield in the playoff final of the Premier League on May 29.