Batter-Baserunner Interference

Question
ASA - Batter bunts and is called out for interference for running inside the baseline. Umpire states that runner must run in foul territory.

What constiitutes interference on this play?

Answer
Thanks for the question.

The running lane exists from 30 feet to first base (which is also a distance of 30 feet.  Fast pitch bags are 60 feet apart typically.)

The runner can run down the line anywhere provided they are not interfering with an defensive person's attempt on a play.  However at 30 feet, they MUST run within the running lane.  Now simply not running in the lane is not interference, the runner must be in the way of a play... ANY play could get her called out for interference... and usually, like you say, it occurs on a bunt where the runner runs in the throwing path of the catcher, and you're past the 30 foot mark.  If it's before the 30' lane, it's an umpires judgment if interference occurs.

I hope this helps answer your question!  If not please reply.