At the highest level of play in the NFL and NCAA, the one constant in all formations is the offensive line, consisting of the left and right tackle, left and right guard, and a center. These five positions are often referred to collectively as the "line", and have the primary role of blocking. By rule there must be two additional players on the line of scrimmage called Ends. These players are eligible receivers and may play near the linemen (tight ends) or farther away (split end or wide receiver). Most teams play additional players near (but still off) the line of scrimmage to act as extra pass receivers.