Pushing in football is when players attempt to move opposing players by pushing into them with their bodies. Football is a contact sport, so it's inevitable that hits, pushes and charges are permitted during the game. Players are allowed to be aggressive to other team members in order to keep them away from the ball or prevent them from making a run down the field.
Pushing occurs on every single play, regardless of the score or situation. Every defensive formation consists of blocking out their opponents. Defensive players push away opponents to keep them away from the quarterback. It's a natural part of the game. They try to keep players from moving into open positions and away from scoring opportunities. Pushing occurs when a player charges another, hitting him directly on his shoulders with enough power and force to move him backwards or tackle him entirely. Pushing players can get dangerous, so it's important that players perform pushes with as much caution as they can without getting injured.
Although pushing is permitted, illegal contact is not permitted during games. Illegal contact occurs when a player is still making significant contact with a receiver after the receiver crosses five yards over the line of scrimmage. The official will call a penalty if this occurs.