Everyone has no doubt heard this story and maybe seen some video of it somewhere. I checked it on Wikipedia and there was the story, thought others might find it interesting:

Playing with The Who[edit]
On November 20, 1973, The Who were opening their Quadrophenia US concert tour at the Cow Palace in Daly City, a suburb just south of San Francisco. Halpin, a 19-year-old who had recently moved to the area from Muscatine, Iowa, was there with a friend using tickets they had bought from a scalper. They arrived at the show thirteen hours early to get good seats.[2]

The Who opened the show with three of their earlier hits before launching into material from Quadrophenia, playing eleven of the album’s seventeen songs and then continuing on to other hits. About seventy minutes into the show, drummer Keith Moon, whose fondness for drugs and alcohol was legendary, began to falter during "Won't Get Fooled Again", slumped over his drum kit, and passed out. As the house lights went up, Moon was carried offstage by roadies, who placed him in a shower in an attempt to revive him. Their efforts worked. An injection of cortisone got him back onstage after approximately a thirty-minute delay.[4]

The show continued with "Magic Bus". The percussion of the song’s opening verses consisted only of Moon hitting two wooden blocks against one another. However, when the drums were actually required, Moon only played for a few more minutes before passing out again. He was carried off—this time not to return. Guitarist Pete Townshend later said in an interview that Moon had consumed large tranquilizer pills, meant to be consumed by animals, with a large volume of brandy.[5]

The remaining three band members then played "See Me, Feel Me", without drums, with vocalist Roger Daltrey adding a tambourine for percussion. The song received a huge response, and Pete Townshend thanked the crowd for putting up with a three-quarter-strength band. Instead of leaving the stage, though, Townshend asked the crowd, "Can anybody play the drums?" He repeated the question, adding forcefully, "I mean somebody good!"[6]

At this time, Halpin and his friend were at the left edge of the stage, and his friend, Mike Danese, began noisily telling the security staff, "He can play!" In truth, Halpin had not played in a year, but Danese made enough of a commotion that he had attracted the concert's promoter, Bill Graham.

“ Graham just looked at me and said, "Can you do it?" And I said "Yes," straight out. Townshend and Daltrey look around and they're as surprised as I am, because Graham put me up there."[2][4] ”
Halpin was given a shot of brandy for his nerves before sitting at his first drumset since leaving Iowa.

“ Then I got really focused, and Townshend said to me, "I'm going to lead you. I'm going to cue you."[4] ”
Daltrey introduced him as "Scot", and went straight into the riff of "Smokestack Lightning". This was a very loose blues jam, Halpin's drum work fitting in well enough, and it shortly became "Spoonful". Less successful, however, was his contribution to the more complex "Naked Eye", and he failed to provide the contrasting tempos despite Townshend attempting to give him instructions. Halpin did not look at all flustered, though, and established a steady beat throughout. The show ended after "Naked Eye", and Halpin took a center-stage bow with Daltrey, Townshend, and bassist John Entwistle. Afterwards, he was taken backstage, along with his friend Mike, and given a Who concert jacket, which Halpin said was stolen later that evening.[4]

In later interviews, Daltrey praised Halpin's ability, claiming that the "papers missed it". Interviewed by Rolling Stone, Halpin admired The Who's stamina, admitting "I only played three numbers and I was dead."[7] On January 27, 2009, The Who posted a link on their website announcing a memorial blog in memory of Scot Halpin.[8]

http://en.wikipedia.org/wiki/Scot_Halpin