Crowd control
The combat encounters comprising a raid usually require players to coordinate with one another while performing specific roles as members of a team. The roles of Tank, Healer, and Damage Dealer are known as the "Holy Trinity" of MMORPG group composition. Other common roles include Buffing, Crowd control, and Pulling (selectively choosing targets with which to initiate combat). A raid leader is often needed to direct the group efficiently, due to the complexities of keeping many players working well together.