The England youth international was assaulted in the tenth minute after a fan ran onto the pitch and attacked the 23-year-old from behind.
When the individual was led away by security 15,000 Blues supporters clapped him.
Speaking of the fan attack, Smith said: "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.
"(Grealish) is a mature lad, has matured an awful lot and the way he handed 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 him to distract him.
"The players' safety is paramount, they are going 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 today.
"It doesn't help to have people applauding him. It's disgraceful, we have to educate society a little bit.
"I like to think most of the fans know it's wrong. As people and human beings 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."