Unusually for Deep Purple, the song does not contain a guitar solo, but a bass solo played by Roger Glover. "Fireball (Take 1 - Instrumental)," a bonus track on the remastered album, features a guitar solo near the end, after the fade-out of the original version.

It is one of the few Deep Purple songs to feature Ian Paice using double bass drums. When performed live, a second bass drum is added to Paice's drum kit by a stagehand, and removed after the song's conclusion.

The song begins with the sound of an air conditioner being turned on, recorded by assistant engineer Mike Thorne. Roger Glover suggested to engineer Martin Birch that the sound of a machine starting up would be a good way to begin both the song and the album, but Birch could not think of anything available that would fit the purpose. Thorne suggested the sound of an air conditioning unit and duly recorded it to the band's delight. At the time, the members of Deep Purple claimed that the sound was produced by a "special" synthesizer.

The song was one of several based on Ian Gillan's real life experiences. "She was a complete mystery to me. This is another tale of unrequited love", was the singer's comment on the song's subject.

The song shares similarities with Canadian band Warpig's "Rockstar," released on their self-titled debut album in 1970.

A promo clip was made for the song, consisting of the band miming to the studio recording in front of a dancing audience. The notes Jon Lord is seen playing do not correspond to the music, and Ritchie Blackmore plays his guitar with the back facing out.

Czech heavy metal band Arakain covered the song on their album Legendy in 1995, as "Karambol". This version is a half-step lower than the original, and does not feature keyboards.

...
Wikipedia