Metalcore is a broad fusion genre of extreme metal and hardcore punk. The name is an amalgam of the names of the two genres, distinguished by its emphasis on breakdowns, which are slow, intense passages that are conducive to moshing. Pioneering bands, such as Hogan's Heroes, Earth Crisis, and Integrity, lean more toward punk, whereas latter bands—Killswitch Engage, Underoath, All That Remains, Trivium, As I Lay Dying, Bullet for My Valentine and The Devil Wears Prada—lean toward metal. Sepultura, who has been credited to "laying the foundation" for the genre, and Pantera, who influenced Trivium, Atreyu, Bleeding Through and Unearth, have been influential in the development of metalcore.
Black Flag and Bad Brains, among the originators of hardcore, admired and emulated Black Sabbath. British street punk groups such as Discharge and The Exploited also took inspiration from heavy metal. The Misfits put out the Earth A.D. album, becoming a crucial influence on thrash. Nonetheless, punk and metal cultures and music remained separate through the first half of the 1980s. Cross-pollination between metal and hardcore eventually birthed the crossover thrash scene, which gestated at a Berkeley club called Ruthie's, in 1984. The term "metalcore" was originally used to refer to these crossover groups. Hardcore punk groups Corrosion of Conformity, Dirty Rotten Imbeciles and Suicidal Tendencies played alongside thrash metal groups like Metallica and Slayer. This scene influenced the skinhead wing of New York hardcore, which also began in 1984, and included groups such as Cro-Mags, Murphy's Law, Agnostic Front and Warzone. The Cro-Mags were among the most influential of these bands, drawing equally from Bad Brains, Motörhead and Black Sabbath. Cro-Mags also embraced straight edge and, surprisingly enough, Krishna consciousness. Other New York metal-influenced straight edge groups include Crumbsuckers who formed in 1982. 1985 saw the development of the hardcore breakdown, an amalgamation of Bad Brains' reggae and metal backgrounds, which encouraged moshing. Agnostic Front's 1986 album Cause for Alarm, a collaboration with Peter Steele, was a watershed in the intertwining of hardcore and metal. During this time, thrash metal groups began to borrow a great deal from hardcore punk, and in 1987 Metallica paid tribute to Discharge and Misfits.