One of the best examples of inertia at work occurs in football. Quarterbacks are protected by offensive linemen, who are immense and have tremendous mass. It takes an incredible amount of force to move these linemen out of the way. But offensive linemen face equally enormous defensive linemen whose job it is to get through their protective wall and harass the quarterback. In this scenario the offensive linemen represent inertia at rest and the defensive linemen represent inertia on the move.