Villa branded the assault as “cowardly” after Grealish was punched 10 minutes into a match in which he then scored the winner for a 1-0 triumph.
Then just hours later at the Emirates an Arsenal fan shoved Chris Smalling in an attempt to join the celebrations of the second Arsenal goal in their 2-0 win over Manchester United – a clear sign that stewarding is failing to keep players safe.
Manchester United manager Ole Gunnar Solskjaer said: “I did not see exactly what happened, but there should not be a place for somebody to run onto the pitch.
“It was not nice to see. We will play football; they can watch.
“It is one of those things we don’t want to see.”
After the Birmingham fan was banned for life, Smith said: “Some mindless moron has gone on the pitch and attacked Jack.
“Then you’ve got 15,000 idiots clapping him, which doesn’t help the matter. That’s disgraceful.
“The way Jack handled it was excellent.”
In a statement, Villa said: “The club is appalled by the disgraceful attack on Jack Grealish.
“A line has been crossed by this cowardly on-field assault on a player, which is unprecedented in English football.”
Birmingham manager Gary Monk said: “The most important bit is that Jack Grealish is all right.”
Arsenal confirmed that their supporter had been arrested and would also be banned for life, with manager Unai Emery adding: “I don’t want that.
“We can enjoy our supporters but we don’t need to have to deal with that aspect.”
The two incidents come after Rangers defender James Tavernier was also attacked by a Hibernian fan in the 1-1 draw at Easter Road on Friday.
Solskjaer felt his first defeat in the Premier League at the 13th hurdle hinged on a very different shove – the weak one Alexandre Lacazette was given by Fred to earn the decisive penalty.
“I don’t think it was a penalty,” he said.
“I don’t think there was any contact big enough to warrant a penalty. Fred must be very strong.”
Three points for Arsenal leapfrogs them above United and now third-placed Tottenham, just one point in front, are firmly in their sights.
When asked if the Gunners could catch their rivals, Emery said: “Yes. But we were positive when we were struggling in the table with a bigger difference.
“Now, after this victory, there is no change.
“We are continuing and it is going to be difficult but our style is to take things game by game. Being consistent is very important.”