There's a 10 second run off if the offense commits a false start (or possibly any penalty, not sure on specifics) if the clock is moving, I believe inside of two minutes.  There's no run off if the previous play was an incompletion or play that went out of bounds.

 

It's a rule to ensure the offense doesn't commit a cheap penalty to stop the clock.

 

I don't remember the penalty at the 1:27 mark, but there was a run off for the false start at the :45 mark, and he did announce the run off.

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