Man Down
Man Down is a term used in Live Action Roleplaying to indicate when someone has been hurt. This usually happens during combat when someone gets an unlucky blow of some sort or they trip or fall over in the heat of the game.
In all reputable systems it is important that when "Man Down" is called it is obeyed swiftly and everyone engaged in combat (or whatever) immediately stops what they are doing. Anyone may call Man Down. Sometimes "Time Out" is used in this situation rather than Man Down.
All reputable roleplaying systems that involve combat of any description (especially those which involve playing in woods and other out of the way places), will have trained first aiders and first aid kits on all adventures.
All this sounds rather alarmist when in fact the most common injuries are minor cuts and bruises such as anyone running around woodland might expect to get. There are occasional twisted ankles and asthma attacks. The most serious injury I've ever heard of was a broken bone when someone fell backwards into a tree branch. However the practice of having a first aider present is common to all "outward bound" style activities into which category many live roleplaying games could loosely be said to fall and it should be remembered that many Live Roleplaying occasions involve large numbers of people (The Gathering, which is the largest, has 3,000 attendees) in which situations the presence of first aiders and well-understood procedures for dealing with injuries are vital.