Sometimes the rockingest rock moments happen when the performers need a little help. Here, based on an epic Reddit thread, I present some performances in which fans join their favorite bands onstage -- and rock.
Weezer - "Undone (The Sweater Song)"
Weezer, live in Japan, brings a fan up to play acoustic guitar.
U2 - "All I Want Is You"
Blind guitarist Adam Bevell went to a U2 show in Nashville. His brother-in-law had made Bevell a sign reading "BLIND GUITAR PLAYER. Bring me up." So Bono brought him up for an encore. They performed "All I Want Is You," Bevell's wedding song, and Bevell walked away with Bono's guitar. For more on the story, read this report (the first video in that link has an interview with Bevell and some extra footage of the performance).
Green Day - "Basket Case"
In this Manchester performance, Green Day recruits fans to play drums, bass, and guitar for a jam session. And it works. (Beware, some salty rock 'n roll language is used. After the fan-band does their thing, the main band returns to play "Basket Case.")
Metallica - "Blackened"
On Metallica's thirtieth anniversary as a band, they invited a couple of metal musicians onstage to perform. Shredding ensued. This video is rather long, as it tells the whole story, but it's pretty fun watching them onstage!
Billy Joel - "New York State of Mind"
In this phone video, audience member Michael Pollack joins Billy Joel onstage to perform a classic.
The Who - Cow Palace Show
Keith Moon, drummer for The Who, passed out during a performance at Cow Palace, reportedly due to a heavy dose of tranquilizers and brandy. Fan Scot Halpin took his place and played three songs with the band, earning him Rolling Stone's "Pick-Up Player of the Year Award."