Defensive alignments are usually titled numerically; the first number refers to the number of players who serve primarily as blockers, the second number referring to the number of players serving primarily as blocking and tip coverage players and the third are the players in the back court (2 - 1 - 3). When only two numbers are in the designation (2 - 4), the number represent the blockers and backcourt players. The 2-1-3 defense is one of the two major defensive alignments, the other being the 2-4. Most other defensive alignments are adaptations of these.