In the NFL, the most common penalties that result in the loss of a down are intentional grounding and illegal throw, which occurs when a pass is made after the ball has passed the line of scrimmage. When a team loses a down, the official indicates it by placing both hands behind their heads. The losing team will then have to start over with a first down.
Losing a down because of an illegal motion can also happen if the player who makes the motion is not identified as an eligible receiver before the ball is snapped. In this case, the play would not be dead until the ineligible receiver was declared out of bounds. Losing a down for unsportsmanlike conduct means the player acted in an inappropriate manner during a play. Examples include kicking a player, hitting a player with intent to injure, or using excessive force against another player. A penalty flag may be thrown for unsportsmanlike conduct, but it cannot result in a loss of down.
Finally, a loss of down can occur because one member of a team is injured and cannot continue. For example, if a player goes down during a running play, the referee will signal for a medical timeout unless the injury appears serious. During the medical timeout, players cannot be substituted into or out of the game. Once the medical staff determines that the player can continue, they return to the field of play and the down ends for that player.
A football player is down when a certain portion of their body makes contact with the ground. In the case of specific penalties, such as an illegal forward pass, a player is also called down. The out of bounds procedure is the same as when a player is down: the ball is placed at the yard line, and the player is ejected. These are commonly called automatic penalties.
An up-and-coming player will often be described as a "down" player because they tend to play below their actual ability level while still on the roster. This is due to the fact that coaches do not want to hurt a player's feelings by releasing them, so they place them in position where they have a chance to see action, but aren't considered important enough to keep around during practice or games.
There are several ways for a player to become a down target. The most common method is through penalty flags. If a player commits a foul which results in a free kick, that player has become a down target. Many times players will become down targets if they enter the field of play with the ball, since it is assumed that they will lose control of it and be taken out by a defender.
Players can also become down targets if they appear to be injured during a game. Coaches will often use this as a way of getting a player off the field without having to actually remove them from the game.
When a player is tackled by the defense, he is usually knocked down. If an offensive player touches the ground with a portion of his body other than his hands or feet in the NFL, he is down if a defensive player touches him. If a player in control of the ball fumbles it out of bounds, he will down the ball. A player can also be declared down if the referee signals for a play to begin immediately after the ball is dead; this allows time for any injured players to be attended to.
In basketball, a player is considered down when he has touched the court with at least one hand and cannot get up before the whistle is blown for the next possession by either team. This does not have to be the fault of the defender; if a shooter is missed, or receives a charge from a non-shooting player, they must go to the bench to recover.
A player is considered down in ice hockey when he is hit into the boards or slides into the net and cannot get up before the whistle is blown for the next faceoff. The only exception is when the player is attempting to shoot and is hit by a skater who has not fully committed to the check. At that point, the player can continue to skate with the puck or drop back to let the attacker try to score.
Down positions are important because they give defenders time to react to what is happening on the field or court.
These are known as kneel downs or quarterback kneels. The quarterback kneel is similar to what happens in a chess game when one player realizes that no matter what they do, their opponent will be able to checkmate them in a few moves. It's a surrender, but in this situation, the winning side takes the initiative rather than the losing side.
This falls under the category of declaring himself down. This is handled in Rule 7, Section 2, Article 1-d-1: Unlike in the NFL, the ball carrier cannot fall to the ground and then get back up to resume play. When you contact the ground with anything other than your hands and feet, the ball is dead.
The number of players on the field limits how many players can be down at once; typically, only one player can be downed per play. A player is considered down until the ball is advanced past him. At that point, he can start again on the next play.
The term "downed player" also refers to any player who is unable to continue playing because of injury. If a player is injured and cannot continue, then it does not matter which part of his body was affected. If a player is unable to get up after being touched by a defender, he is out for the play. He will not reenter the game unless another player is hurt or forced out of the game.
In college football, certain penalties are assessed to a down depending on what part of the player's body was hit. For example, a player is penalized for a foul when he is touched by a defender. The penalty depends on where on the body the contact is made: a flag should be thrown if a helmet makes contact with the player; otherwise, no penalty is called.