A beat 'em up (also known as brawler and, in some markets, beat 'em all) is a video game genre featuring hand-to-hand combat against a large number of opponents. Traditional beat 'em ups take place in scrolling, two-dimensional (2D) levels, while some modern games feature more open three-dimensional (3D) environments with a larger number of enemies. Gameplay tends to follow arcade genre conventions, such as being simple to learn, but difficult to master, and the combat system is typically more highly developed than other side-scrolling action games. Two-player cooperative gameplay and multiple player characters are also hallmarks of the genre. Most of these games take place in urban settings and feature crime-fighting and revenge-based plots, though some games may employ historical, science fiction or fantasy themes.
The first beat 'em up was 1984's Kung-Fu Master, which was based on Hong Kong martial arts films. 1986's Nekketsu Kōha Kunio-kun introduced the belt scroll format employed extensively by later games, and also popularized contemporary urban settings, while its Western localized version Renegade further introduced underworld revenge themes. The genre then saw an interval of high popularity between the release of Double Dragon in 1987, which defined the two-player cooperative mode and continuous belt scroll format central to classic beat 'em ups, and 1991's Street Fighter II, which drew gamers towards one-on-one fighting games. Games such as Streets of Rage, Final Fight, Golden Axe and Teenage Mutant Ninja Turtles are other classics to emerge from this time. In the late 1990s, the genre lost popularity with the emergence of 3D-polygon technology.