The president of the Vigils is always a football player.
The current president of the Vigils is Carter. His job is to keep order at the meetings of the secret society, and, in the small room behind the gymnasium which is their meeting place, the sound of his fingers snapping brings silence to the proceedings immediately. The president of the Vigils is always a football player because he must have "the muscle" to keep things in control for Archie Costello, who, as the Assigner, wields the true power over the organization.
The Assigner is the brains of the operation, while the president provides the brawn. Nobody messes with the president because of his raw physical strength, but everyone knows the real head of the Vigils is the Assigner, who masterminds the elaborate pranks undertaken by the group and is "always one step ahead of them all" (Chapter 5).