From GameWatcher: “Rocket League’s latest achievement may well be its greatest. This wacky, colourful driving/sports hybrid has attained a befuddling 50 million players over the course of its lifetime! Granted, this does include alter-accounts, re-purchases and whatnot, but still.”
Source: N4G PC Rocket League Player Count – Psyonix's Smash Hit Reaches 50 Million Players