“Following the incident on the pitch involving an attack on an Aston Villa player; a man has been arrested and [is] en route to a custody block,” West Midlands Police said on Twitter.
Aston Villa said they were “appalled by the disgraceful attack” on Grealish, adding that a “red line has been crossed by this cowardly on-field assault on a player, which is unprecedented in English football.
“We trust the perpetrator will feel the full force of the law and the authorities investigate the circumstances surrounding today’s deplorable incident,” the club said in a statement.
Birmingham apologised to both Grealish and Villa in a statement of their own and banned the fan for life.
“What happened has no place in football or society,” the club added.
“Jack is a Birmingham lad and regardless of club allegiance should not have been subjected to this – there are no excuses.”
The incident follows another on Friday where a fan confronted Rangers captain James Tavernier on the pitch during the Scottish Premiership game with Hibernian in Edinburgh.
Grealish scored in the 67th minute, and was booked for his subsequent celebrations, as ninth-placed Villa kept their play-off hopes alive.
“The EFL condemns the mindless actions of the individual who encroached on to the pitch at St Andrew’s on Sunday afternoon,” said the governing English Football League.
“It’s a situation no player should ever be faced with.
“Whilst this incident falls within the remit of the Football Association, we will work with all the relevant parties to address the issue of player and match officials’ safety on the pitch and ensure the appropriate action is taken.”
A second pitch invasion took place hours later at Emirates Stadium as Arsenal beat Manchester United 2-0.
A man ran onto the field and made contact with United’s Chris Smalling moments after Arsenal’s Pierre-Emerick Aubameyang scored a penalty.
He then made his way towards the celebrating Arsenal players with arms aloft before being taken away by stewards.