The term 'ROCKER's Rival' can be solved by the three letter word 'MOD'. The MOD movement was a British youth culture that emerged in the late 1950s and early 1960s. It was a reaction against the Rockers, who were known for their leather jackets, motorbikes, and rock and roll music. The Mods were known for their sharp suits, scooters, and soul and ska music. The two groups were rivals, often engaging in physical confrontations.