Blocking is such an important part of strategy in football game. A team cannot win a football game without a strong blockers. Blockers are so important, they exist in all three player units:
Blockers do exactly what you think they would do. They block players on the opposing team from moving toward their teams end zone.
Since both teams employ blockers, blockers usually just block each other. However, a blocker may break free from a blocker on the opposing team. He then has a chance to tackle the ball-carrier.