Aston Villa boss Dean Smith has labelled the fan who attacked Jack Grealish a "mindless moron" while Birmingham manager Garry Monk called for the strongest punishment.
Captain Grealish – who recovered to score a second-half winner – was struck in the ninth minute after a man ran onto the pitch and punched him from behind at St Andrew's.
Villa won 1-0 on Sunday and the individual, who came onto the pitch from the Main Stand, was arrested by West Midlands Police.
Grealish showed remarkable character and maturity to revive Villa's fading Sky Bet Championship play-off challenge and move them to ninth, four points behind the top six.
Smith said: "Security should be better, it's why we kick off at 12pm on a Sunday to keep them out of the pub.
"Unfortunately some mindless moron has gone on the pitch and attacked Jack and then you have 15,000 idiots clapping him as well which doesn't help.
"It's disgraceful, we have to educate society a little bit.
"He is a mature lad, has matured an awful lot and the way he handled the whole thing was excellent. The only way to answer that was to score the winner, which he did.
"We didn't talk about it (at half-time), his mind was totally on the game and I didn't want to distract him.
"The players' safety is paramount, they are going on to the pitch to entertain, that's their job. I'm all for local rivalry but there has to be a line drawn after this.
"I'd like to think most of the fans know it's wrong. As people we have to make sure it doesn't happen.
"I'm very proud with the way he handled it. He gets on with things. He is a terrific lad and terrific footballer."
The Football Association will wait for the referees' report before deciding on a course of action while the English Football League condemned the violence.
Grealish, 23, won the derby when he fired in across Lee Camp from 16 yards after 67 minutes.
Conor Hourihane hit the bar for Villa and Craig Gardner wasted two chances to equalise late on when he shot over and headed wide.
Birmingham boss Monk also blasted the violent act and wants the offender – who will banned from St Andrew's for life – punished.
"I'm not just speaking for everyone at Birmingham but everyone in football, that cannot happen on a football pitch," he said.
"The guy who has done it needs to be punished severely and given the ultimate punishment he can be.
"I've been here a year now and one idiot act does not represent what these fans are. They all feel the same in condemning it.
"A couple of the staff have seen him and made sure he's all right. The most important thing is he is fine."
Birmingham sit 11th, five points from the play-offs after a third defeat in their last five games.
Monk added: "It's a painful one, we're gutted. We felt we did enough to warrant a point. We gave them too much space for the goal and got punished for it."
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