Nottinghamshire Police’s chief inspector Paul Hennessy said: “A 31-year-old man has been arrested on suspicion of assault in connection with this incident. He remains in custody and will be questioned by officers.
“Our enquiries into the circumstances surrounding the incident are ongoing. We have spoken to the player concerned and we are working with both clubs who are supporting us with our investigation.”
The Blades captain was sidelined for the second leg because of injury and was stood on the touchline after Forest secured a dramatic 3-2 penalty shootout victory following a 3-3 aggregate draw, which precipitated a pitch invasion at the City Ground.
Footage shared on social media appears to show one supporter running at the 36-year-old former Forest striker and knocking him to the ground.
Forest have condemned the incident and said in a statement they will “will work with the authorities to locate the individual” and the offender will be subject to “a life ban” from the club.
The incident overshadowed Forest’s win, where the Reds’ victory secured a play-off final showdown against Huddersfield on Sunday, May 29 at Wembley Stadium and the chance of a top-flight return for the first time since 1999.
Sharp branded the individual a “scumbag” but said he would not lose his “respect for the Forest fans”.
“One mindless idiot ruined what was an unbelievable night of football,” he said on Twitter.
“Congratulations to Nottingham Forest on their victory and good luck in the final.
“As an ex-Forest player I will not let one scumbag ruin my respect for the Forest fans.
“Incredibly proud to be captain of this group of Sheffield United players, they gave their all and can hold their heads up high. We will be back and go again.
“Thanks for all your messages and support after the incident.”
The Professional Footballers’ Association added in a statement on Twitter: “We are shocked and appalled by the senseless assault by a fan on Sheffield United’s Billy Sharp. The football pitch is a place of work for our members, this is one of a growing number of incidents this season.
“Matchday security and fan disorder needs to be reviewed ahead of next season, and we will be raising player safety with the clubs, leagues and the UK Football Policing Unit.
“There is no place in football for this behaviour. We recognise that stewards and the police have a very difficult job, a suspect has been arrested, and Nottingham Forest have confirmed the offender will be banned for life.”
They were pushed all the way there, though, after squandering a two-goal lead. After leading 2-1 from the first leg Brennan Johnson gave them a cushion but second half goals from Blades duo Morgan Gibbs-White and John Fleck pushed the tie to extra-time and then penalties.
Brice Samba, who produced a special point-blank save from Iliman Ndiaye late on, then kept out the spot-kicks of Oliver Norwood, Conor Hourihane and Gibbs-White to the delight of a packed out crowd.
The playoff final is on May 29th.