Story courtesy everyrecordtellsastory.com
On This Day In 1973 The Who was playing the Cow Palace near San Francisco in support of their Quadrophenia album. Over an hour into the show, during "Won’t Get Fooled Again", drummer Keith Moon suddenly slumped over his drum kit, and passed out. He was carried out by the road crew and was revived sufficiently to carry on, albeit after a half hour delay. The Who started up again playing "Magic Bus" and Moon played for a short while and then collapsed again.
According to Pete Townshend's autobiography...
“He (Moon) collapsed onstage after taking three elephant tranquilliser pellets. I had to drag him back to his drum kit when he came around; then he collapsed again. At first I thought he may be play acting a little….I didn’t really get upset until later when it became clear he had taken a….potentially fatal substance”. John Entwhistle, Roger Daltrey and Pete Townsend continued without a drummer for "See Me, Feel Me", until Townshend finally asked the crowd, "Can anybody play the drums? I mean somebody good!" In the audience that night was nineteen year-old Scot Halpin. When infamous concert promoter Bill Graham saw Halpin, he looked him in the eye and asked him whether he could do it. Halpin replied “Yes”, was given a shot of brandy, and for the next three songs he was the drummer for The Who, playing "Smokestack Lightning", "Spoonful" and "Naked Eye".
At the end of the show, Halpin received an ovation from the crowd, alongside Daltrey, Townshend, and Entwistle. They even do the can-can. Unbelievably there's video proof!