Blood rule
The blood rule is a rule used in many sports that states that an athlete that receives an open wound, is bleeding, or who has blood on them or their clothes, must immediately leave the playing area to receive medical attention. Though they may be able to play again later, they cannot go back and play again until the wound is taken care of, bleeding has stopped, and all contaminated equipment has been replaced. The main concern addressed by this rule is the spread of infectious diseases like Human immunodeficiency virus (HIV), Hepatitis, and other diseases that  can be spread through the contact of blood. Though there are two options that can be chosen: the first option is that the player be substituted and play resumes, or the official can halt play until the player has returned, the former being the most commonly chosen. In the National Rugby League, the latter option is first employed; play stops whilst the player's medical staff attends to the wound. If the bleeding is not stanched to the referee's satisfaction, the player must then leave the field for further attention. In sports such as association football, a player may  leave the field without being substituted immediately, his team playing short-handed until he re-enters play, is replaced, or the match ends (if the injury cannot be satisfactorily healed and the team is out of substitutions). If a player refuses to leave even though an official requests they do so this occurs, the official will stop play, and if the player continues to stay after play has ceased, the official will enforce the rules for accompanying league, which may include forfeiture of the game. Some sports where this is used are Australian Rules Football, NCAA Baseball, and many  major American sports leagues like the National Hockey League, National Basketball Association, and Major League Soccer.