So... this made ESPN. USL has petitioned IFAB to permit them to experiment with the "concussion substitution" in 2020. What they propose is a new concussion protocol, where a player suspected of a concussion can temporarily be subbed. If the player is cleared, they can return to the field, and the temp sub is pulled. If the player is told they cannot continue, then the temp sub is made permanent, and charged against the team as a regular sub. If they have no subs left, the temp sub is pulled off the field.