here's my understanding of the national mechanic and what UO is used to - the offense basically controls what the U does and whether we go into the holding pattern.
Two scenarios - offense huddles vs. doesn't huddle:
Huddle - only when offensive subs rush quickly to the LOS to create a defensive disadvantage (not everytime the offense subs) - the U comes up over the ball, R checks the defense, if no defensives subs coming in he pushes the U off, if defense immediately reacts with subs then the R holds the U for a moment allowing the subs to get in place.
No huddle - the U is always over the ball - R checks the offense and if no subs coming in, pushes the U off; if offensive subs come in, then we go into the scenario above.
(added) - Team A subs enter after huddle breaks - U comes up either on own or upon signal by R - holding pattern - B has chance to match up
Works well and is consistent with the rule and, yes, the Big 10 is working the game - great guys and excellent officials.