They should codify how long the defense has to make substitution starting when the offense runs new players on the field (and replaced players begin moving off the field. 10 seconds is more than enough time for defense too see what substitutes are coming on... and make their adjustments, including replaced players getting off the field. If the Offense initiates new substitutions, 10 sec clock restarts. Easy for Referee to keep a count and he can demonstrate he's started his count by swiping his arm.
Bielema had defensive replacements walking on field slowly.... and one at a time. Had the replacements walking slowly off the field one at a time. He then went and started taunting USCe team and coach by imitating the Center Judges Signal to hold the snap when standing behind Center on substitutions (i.e., holding both arms outstretched to side) while laughing. It was a ridiculous display by a Head Coach, especially a HC who was intentionally abusing the rule in a highly Unsportsmanlike way who caused USCe to call not 1, but 3 separate TOs with this intentional behavior. He should have been flagged, especially for the ridiculous taunting display - Officials throw Taunting flags on players for celebrating TDs, but they don't throw one on a Head Coach obviously acting in an unsportsmanlike way Taunting his opponent at midfield - utterly ridiculous and that fat pos eminently deserved to be penalized.