A fan spitting at Roger Waters inspired "The Wall.

Yes. That’s the one.

During Pink Floyd’s 1977 show at the Montreal Olympic Stadium, a fan near the front was spitting at the band repeatedly. Roger Waters had enough and spat back at the guy. He was disgusted with himself afterward—and that moment directly led to the idea for The Wall.

The whole concept of building a wall between performer and audience came from that incident. Waters felt separated from the crowd, and the spitting symbolized the breakdown of communication.

So no, it wasn’t a technical malfunction or a riot. It was one angry fan and one fed-up bassist.