Imagine this scenario: Let's say you're a teenager fresh off the turnip truck from the Midwest and newly arrived to the big city. You go to a sold-out arena show hosted by your favorite superstar rock group, when suddenly one of the musicians becomes incapacitated. The remaining band members then pluck you out of the audience to take their fallen comrade's place in the middle of the set, and you end up saving the day.

Crazy fantasy, right? Not if you asked then-19-year-old Who fan Scott Halpin, as that exact series of events happened to him in 1973 when he was selected out of the crowd to stand in for hard-pounding, hard-living drummer Keith Moon for the remainder of the band's program.

On October 20, 1973, Halpin, who had just moved to California from Iowa, had gone with his friend Mike Danese to see the Who perform at the Cow Palace arena, located just outside San Francisco. The pair had arrived hours early to get good seats at the general-admission show, a move that paid off in ways Halpin couldn't have anticipated. The Who were touring in support of their 'Quadrophenia' concept album, and this was the first night of their North American tour. (Lynyrd Skynyrd, then a scarcely known band from Florida, was the opening act.)

As the headliners began their set, Halpin, as well as almost anyone in attendance with eyes and ears, noticed that Moon was unsteady and erratic behind his drum kit. This was a result of the famously overindulgent drummer's ingesting heaven knows what smorgasbord of illicit substances pre-show. (Moon would die of a prescription drug OD in 1978.) About halfway through the set, during 'Won't Get Fooled Again,' the inevitable happened: Moon passed out.

After a moderate delay, the Who's wildman drummer was pronounced fit to carry on, but it turned out that snap medical assessment was premature. Plopped down on his stool, Moon somehow plodded his way through a medium-size chunk of the song 'Magic Bus' when he went down for a second time. At this point, Pete Townshend approached the microphone: "Can anybody here play the drums?" the anguished guitarist called out to the audience, as roadies dragged a zonked-out Moon backstage.

Danese, well aware that his friend Halpin played drums, though he hadn't been behind a kit since moving west, volunteered him for fill-in duty. Surprising himself, the teenager from Iowa agreed to it. The next thing he knew, he was ushered onstage and set up behind Moon's kit, and began working out cues with his idols. Just a few hours earlier, Halpin was trying to secure a ticket for this show, and now he found himself enthroned on the best seat in the house.

Roger Daltrey introduced the newly deputized Halpin to the crowd, after which the frontman and the rest of the group launched into blues titan Howlin' Wolf's 'Smokestack Lightning,' with the 19-year-old handling the beat like a seasoned, if not slightly overwhelmed, pro. Two songs later, his literal 15 minutes of fame over, Halpin received as payment for his work a tour jacket, a mention in the San Francisco Chronicle's concert review and a letter of gratitude from the Who.

One final honor was later bestowed upon the drummer when Rolling Stone named Scott Halpin "Pick-Up Player of the Year" in the 1973 wrap-up issue. These days, Halpin lives in Indiana with his wife and child, and every now and then he likes to fool around with his favorite instrument -- yes, the bass guitar! Now, it makes perfect sense that he would give the drums short shrift these days; after all, how could it possibly measure up?