NU v. Creighton Overturned call

[SperlingPE]

Runners on 2nd and 3rd, one out.
Pitcher is on rubber and steps off.
The count is 0-0 and no pitch has been thrown to the batter, yet.
Bench screams for a balk.
Home plate umpire is shaking his head as if to indicate the balk is not going to be called.
1B umpire calls balk. Runners move up.
Coach from defensive team comes out for an explantion/argument with home plate umpire.
Coach states his case. Umpires confer.
Runners were put back on at 2nd and 3rd.
I did not see what movement the pitcher made to cause a balk call.
My question is what could cause the disagreement between the two umpires (whom I assume both saw the same movement) and the subsequent overturning of the call?

[bob jenkins]

Originally posted by SperlingPE
Runners on 2nd and 3rd, one out.
Pitcher is on rubber and steps off.
The count is 0-0 and no pitch has been thrown to the batter, yet.
Bench screams for a balk.
Home plate umpire is shaking his head as if to indicate the balk is not going to be called.
1B umpire calls balk. Runners move up.
Coach from defensive team comes out for an explantion/argument with home plate umpire.
Coach states his case. Umpires confer.
Runners were put back on at 2nd and 3rd.
I did not see what movement the pitcher made to cause a balk call.
My question is what could cause the disagreement between the two umpires (whom I assume both saw the same movement) and the subsequent overturning of the call?

Some Options:

1) Time was out. BU didn't know it.

2) BU saw a move that he thought was a balk, but it turned out to be legal (perhaps BU mis read which foot was the pivot foot).

3) The batter (or other offensive personnel) initiated the balk (batter stepped out, F1 stopped the delivery).