The incident occurred during Saturday's Birmingham Derby, a match which in which Aston Villa prevailed thanks to a winning goal from Grealish himself.
A Birmingham fan has been jailed for 14 weeks after pleading guilty to assaulting Aston Villa star Jack Grealish during the derby between the sides on Sunday.
Paul Mitchell, 27, swung a punch at Grealish when the player's back was turned after Mitchell illegally invaded the pitch at St. Andrew's stadium during the fiercely-contested derby match in the English Championship.
Mitchell also admitted to invading the pitch and has been banned from attending any football match in the U.K. for 10 years. He was also ordered to pay a £350 fine.
Villa remains in the hunt for a playoff place after their win over Birmingham. They trail sixth-placed Derby County by just four points with ten matches to play. Their next fixture is away to Nottingham Forest on 13 March.