A quarterback (QB) is a position in American and Canadian football. Quarterbacks are members of the offensive team and line up directly behind the center, in the middle of the offensive line. A quarterback is usually the leader of the offensive team, and initiates most plays. In addition, the quarterback is responsible for calling the signals before most plays.
The term quarterback has its origin in Scottish Rugby, wherein backfield players, according to their customary distance behind the forwards, were designated "quarter back" (i.e. ΒΌ of the way back), "half back", and "full back". Eventually in rugby the English-Irish nomenclature prevailed, with halfback, three-quarters back, and fullback; in some places, notably New Zealand, the term "five-eighths back" is used as well.