LEARN AMERICAN FOOTBALL: THE PLAYERS

The rules in football allow each team to have eleven players on the field at a time. Teams may substitute players between plays with no restrictions. Each team must start a play on their side of the ball.
The defensive players may take any position they want and can move about their side of the football prior to the play without restriction. Although there are certain defensive positions that have become common over time, there are no specific rules defining defensive positions or roles.
The offensive players, however, have several rules that define their position and what role they may take in the offense.