also quarter-staff, 1540s (quarter-stroke "stroke with a quarterstaff" is attested from early 15c.), stout pole, six to eight feet long (six-and-a-half sometimes is given as the standard length), tipped with iron, formerly a weapon used by the English peasantry. From staff (n.). The quarter likely is in reference to its operation.
It was grasped by one hand in the middle, and by the other between the middle and the end. In the attack the latter hand shifted from one quarter of the staff to the other, giving the weapon a rapid circular motion, which brought the ends on the adversary at unexpected points. [Century Dictionary]