The Rice University Neologisms Database

Etymology : BR stands for "battle rifle", one of the most widely used weapons in the Halo video game series. In the heat of battle when every millisecond counts, most players use abbreviations and slang like this rather than using longer, more formal phraseology in an effort to quickly communicate information to teammates. The initialism originally referred to the weapon itself, but through zero derivation came to include the verb form describing the weapon's use.