The film is based on a non-fiction novel by Frank Elli. The novel described a real riot that took place in an Arizona state prison.
There's a Dirty Dozen reunion in this movie. As well as starring as 2 convicts in Riot, Jim Brown and Ben Carruthers both starred as 2 of the 12 military convicts sent to Nazi occupied France on a suicide mission in The Dirty Dozen. They became friends on set, with the cast also regularly socialising together off set.
Second crime film pairing Gene Hackman with Jim Brown, the other being THE SPLIT the previous year.
The plot about the rioters trying to get better prison conditions (which is just a front for the escape) was in the Don Sigel film Riot in Cell Block 11.