In the game of football, when a player breaks a rule, a foul is called and penalty, or punishment, is given. This usually means loss of yardage.
When a referee wishes to signal a foul, he tosses a gold flag onto the field. Should an offensive player be penalized, his or her team loses yards. If the defense is penalized, the offensive team is awarded extra yards.

Here are some common types of fouls for which penalties are imposed.

You may not tackle or hold on to any part of your opponent’s uniform unless he or she is carrying the ball. You may, however, block players who don’t have the ball, but you may not hit a blocker’s head.
If you fight with an opponent you will, in addition to earning a penalty for your team, be disqualified.

You may not hold on to any part of an opponent’s helmet.

Once a referee blows a whistle, before each down, the offense may not take more than 25 seconds to snap the ball.

When a quarterback throws away the ball just to avoid being sacked, it’s known as intentional grounding and it’s a foul. (Sack means when the quarterback still has the ball and he’s tackled behind the line of scrimmage.)

You’re not allowed to move across the line of scrimmage before the ball is put into play by the center.

You’ll be penalized for a late hit. This means that you may not tackle an opponent after the referee has blown the whistle.

Just as you can expect to be punished if you break a law in your community, so too can a professional football player who breads one of the rules of the game.