If during a game, a player is injured and no trainers or first-aid providers are available but one of the referees has extensive medical training; is it appropriate for that referee to assess the injury and provide advice to the coach on how to treat the injury or instruct the coach to seek emergency medical care for the player?
USSF answer (February 20 2010):
Only as an absolute last resort. In this litigious society of ours, a referee who is not a licensed medical practitioner would be well advised to stay out of any medical emergency that occurs during the game that referee is working.
The situation is generally controlled by state law (sometimes called a “good Samaritan” law, but also laws that cover specific professions). In some states, you are expected to perform whatever emergency services you are trained/certified to do. An EMT who is also a referee must therefore take off his referee hat and put on his EMT hat if faced with a serious injury on the field. Otherwise, stay out of it and remember that there are other important referee things you could be doing while staying out of it.