Interference Clarification

Question
This is ASA Rec Women's softball with stealing allowed.  I was playing 3rd base, Runner on 2nd base.  Ball was pitched, catcher bobbled the ball, runner on 2nd takes off attempting to steal to 3rd base.  Catcher was throwing to me at 3rd in attempt to get the base runner out.  Readying myself to catch the ball, I stepped in front of 3rd base to ready myself for the tag.  Runner slides, but my foot stops her from reaching 3rd base.  Umpire declares dead ball, awards the base to the runner and calls me for interference.  I was confused on the call and unclear on whether this was actually interference because it was not a batted ball, she was attempting to steal.  Could you provide me with clarification and where exactly in the ASA rulebook this is stated.  Thank you.

Answer
Hi Corrine,

the question is did you have control of the ball before you blocked the base?  It doesn't sound like you did?  If not we have obstruction (not interference that's caused by the offense) and we protect the runner to the base they would have made.  "About to receive" the ball doesn't matter in ASA, you must have control.

Read RS 36 Obstruction.

If you had control of the ball you can legally block the base.

Mark