For questions generally related to the general responsibilities of team's or player's coaches, such as strategy decisions, player development, team makeup, etc. Questions should be tagged with the specific sport referenced.
In most sports, a coach is a senior supervisory role, generally responsible for the player selection, training and general strategic decisions of a sports team. Franchises in major-league and collegiate sports often have several coaches, with one "head coach" managing several "assistant coaches" and various specialized coaches overseeing the players in a particular field position.
The head coach is typically the "general manager" of the team. He is hired by the team's owners (in a professional franchise) or board of administrators (in interscholastic sports), and is responsible for all major decisions involving the recruiting and releasing of players, active roster composition, training regimen and schedule, basic team strategy including the playbook, and in some sports calling plays from the sideline.
He can delegate some or all of these responsibilities to his assistants where available; depending on the sport, a head coach may have offensive and defensive specialist coaches, and even training coaches focusing on one specific aspect or player position in the game.