It just happened in the 10th minute if a man wearing a cap came on into the pitch from the home section before swinging his arm Grealish’s face.
The man, who had been wearing a Birmingham City coat, blew kisses towards the Audience as he had been led away by stewards.
West Midlands Police said a man was arrested following the incident.
Villa captain Grealish stumbled the St Andrew’s turf before being helped up by players in the teams and has been able to last.
The EFL issued a statement saying it condemned the man’s actions, adding:”It’s a scenario no player should ever have to deal with.
“Individuals playing in the game has to be able to do so safe in the knowledge they won’t be exposed to the kind of behaviour.
“While this incident falls within the remit of the Football Association, we will work with all the applicable parties to deal with the dilemma of player and match officials’ safety on the pitch and make sure the proper action is taken.”
Former Birmingham midfielder Darren Carter said on BBC WM radio:”This is a rivalry and you get enthusiastic, but you should not come on to the pitch. This is diabolical behaviour.”
On Fridaya man was arrested after Rangers’ James Tavernier was faced with a spectator during Friday’s Scottish Premiership draw Hibs.