The question is what happens if a team has used all its players that are capable at a certain front row position and the player on the field needs to go off temporarily for either blood or a head injury assessment.
REMEMBER THAT TEMPORARY REPLACEMENTS FOR HEAD INJURY ASSESSMENT ARE ALLOWED ONLY AT THE SENIOR ELITE LEVEL AND MUST HAVE WORLD RUGBY AUTHORIZATION. This is not happening at any of the competitions that lead to USA Championships at any level.
If the front row player is only going off temporarily, the player may be replaced by some other substitute and uncontested scrums will be ordered.
If the player turns out to be gone permanently (after the treatment or assessment), the temporary sub will need to leave the game [per 3.5 (k)] and scrums will continue uncontested.