What does "crossbar" mean?

Crossbar: A transverse bar or piece, as a bar across a door, or as the iron bar or stock which passes through the shank of an anchor to insure its turning fluke down. Russell. Crossbar shot, a projectile which folds into a sphere for loading, but on leaving the gun expands to a cross with a quarter ball at the end of each arm; -- used in naval actions for cutting the enemy's rigging.