Paul Mitchell stormed the pitch at St Andrew’s during Villa’s match with Birmingham on Sunday afternoon and threw a punch at Grealish from behind.
He pleaded guilty to charges of assault and invading the pitch and will be sentenced by Magistrates this afternoon.
Mitchell’s lawyer told the court his client had not been drinking and that he had only ran on to the pitch to ‘whip up the crowd’.
Meanwhile, prosecutor Mr. Purser, who was speaking on behalf of Grealish, revealed Mitchell called the 23-year-old player a ‘kn*b’ as he was escorted off the pitch following the assault.
The court was told that Mitchell had been forced to move out of his home in Birmingham after he received death threats.
“This is a high profile case, captured on national television,” Mitchell’s lawyer said.
“My client’s young family have had to leave their home and move out of Birmingham in fear of serious harm or death.”
In a statement read out on behalf of Grealish, the court was told that the Villa midfielder was shaken up by the events at St Andrew’s
Mr Purser, said: “Jack Grealish was shocked and scared because if this person was brazen enough to get onto the pitch, what else could he do?
“He didn’t know the person who assaulted him and didn’t antagonise Birmingham City supporters.
“It could have been worse had the person had a weapon.
“It was an unprovoked assault on someone doing his work. There was pain, discomfort and shock.”
Mitchell’s lawyer added: “It has brought shame upon his family and the club he has supported as a child. [He has been] a season ticket for over 20 years.
“He has apologised to Aston Villa and of course to Jack Grealish.
“This was totally out of character. He cannot explain what came over himself yesterday morning.
“His initial foolish intention was to go onto the pitch to whip up the crowd.
“He is certainly remorseful today. He is a man with a partner, they have a two-year-old together and they’re expecting their second child.”
Mr Purser also told magistrates that Mitchell verbally abused Grealish after attacking him.
“The officer who was carrying Mitchell off the pitch said Mitchell thought Mr Grealish was a nob,” he said.
“Mitchell claims he was not intoxicated and was with his father and did it as a joke.
“He did say he was remorseful.”
Both the EFL and Birmingham City Football Club had condemned Mitchell’s behaviour in separate statements before his appearance in court.
Grealish did not retaliate to the assault and went on to score the only goal of the game to secure a 1-0 win for Villa in the Second City Derby.