A pre-determined strategy in football comprised of offensive or defensive formations, developed by a team's coaching staff, which is dependent on the specific circumstances of a game and the style of football employed by a team.
A football team's playbook is typically a collection of various offensive and defensive schemes. That is, a set of strategies involving specific formations and plays the team utilizes on the both the offensive and defensive side of the ball. There are a large and varied number of schemes that exist in football-as the game evolves variations on existing schemes and new, more exotic schemes emerge.
Typical defensive schemes include the 3-4 and 4-3 defense, Man-to-man and zone (coverage) defenses. Offensive schemes include the West Coast, Spread and Pistol offenses.
Schemes will often be used to describe a team's overall offensive or defensive strategy, but are often broken down further. For instance, for a particular play, the center may call out a particular blocking scheme to the offensive line that is consistent with the play being called. Scheme and strategy are almost interchangeable terms, with the exception being that schemes always possess a specific intent, direction and expected outcome.