Quadropehnia (wikipedia), from 1979, based on the 1973 "The Who" rock opera albumn of the same name, shows 1960s UK youth rivalry, between the Mods and the Rockers (Mods; Rockers) in amongst the story of Jimmy and his attempts to gain love.

From this distance in time (30 years since it was made, over 40 since it was set) and space (other side of the Earth) it feels like a very different culture, and yet the film manages to capture enough of the atmosphere that you can empathise with Jimmy and the Mods and their motivation for their actions, and also get a sense of the causes of the underlying rivalries (mostly a need for young men to choose sides). It also goes some way to explaining hits like the Ray Columbus and the Invaders song "She's a Mod" (a NZ band, that made it big in Australia), which went on to become a classic still regularly played on the radio when I was growing up.

It's particularly interesting to see a "scooter gang" (the Mods, who ride bling'd out Italian scooters), with Italian scooters portrayed as much more than a utilitarian cheap form of transport, but raised to highly customised statements of culture. In contrast the Rocker's motorcycle gang looks and approach is much easier to understand given subsequent history with the motorcycle gangs being villified by the mainstream media.

Like many influental films, several of the cast have gone on to other things, including Phil Daniels (playing Jimmy) who has a long TV career, Leslie Ash (playing Steph, the love interest) who also has a long TV career, and Sting (playing Ace Face, the idol) who has a long career in film and music. Even actors like Timothy Spall turn up (as the projectionist).

The 2 disc set I bought (region 2, 4, 5 -- so presumably the Region 2 re-release that the wikipedia page talks about) has both a feature commentary (director and two "headline" actors) and a "making of" documentary. It'll be interesting to see what additional light the commentary can shed on the culture depicted or the films influence.