[AtlUmpSteve]

I also don't find the rule vague. The point is that all conditions for the LBR have been met; ball in circle, BR has passed first, runner has an opportunity to recognize and react immediately.

Let's realize that the BR overrunning first is an exception. In every other case when the LBR goes in affect, a runner is either 1) stopped on a base, and must now judge immediately to leave or stay, putting herself in jeopardy if she leaves, 2) stopped off a base, is in jeopardy, and must judge immediately which direction to move, or 3) in motion between bases, in jeopardy, and may continue to advance or return, with one stop or change of direction available. The one major difference about the BR overrunning first is that these runners are all in jeopardy (well, possible exception of runner stopped on the base that doesn't leave).

In the case of the BR that overruns first, the general rules grant an immunity from jeopardy; that runner may return safely, has an extended opportunity to judge the situation that no one else gets, and, therefore, has been given a shorter leash by the LBR. If the ball gets in circle while that runner is returning without jeopardy, the rule makes that runner make the change of direction immediately upon recognition that conditions have been met. Since this runner is NOT between bases, a stop or reversal is not an option; the choices are to continue to first, thus committing to first, or immediately heading to second. This is only fair to balance the special protection granted the runner returning to first without jeopardy, and gives the defense a fair opportunity to see her decision, then move on when no action is taken.

The NCAA coaches saw it differently; they created a special game situation where the runner gets immunity and still can run a trick play if returning within 3' either side of the foul line. That forces umpires and players to stare at the runner until she fully (and often slowly) returns to the bag and stops. No one can move on; we stand in our calling position, unable to rotate to our starting position for the next play. In a three umpire crew with no other runners, PU stands at attention half way up the foul line, U1 stands in fair territory facing first, and U3 stands on the infield side of 2nd, at attention, simply waiting to be able to rotate to get into next position. It looks like a dummy drill. In ASA of NFHS, since the runner is committed, the players can get relaxed and ready for the next batter, and all but one umpire can begin to rotate to the next position. Play over, move on.

So, the special condition attached to BR overrunning first has a reason, and isn't retroactive; it just requires an immediate reaction from the protected runner when all the conditions are met.