pick off play at first base

Question
ASA fast pitch - Here was the situation - pick-off play at first base. The second baseman comes in behind the runner and places her foot on the ground at edge of the base between the runner and the base. The runner returns to first base and has her foot on the second baseman's foot instead of the base.The runner is tagged without touching the base. Is the runner safe? The umpire's ruling was safe because the secondbaseman's foot was considered part of the bag.  Is this correct? That seems totally outrageous to me.  (I was the secondbaseman and couldn't beleive the call) Thanks for the help!

Answer
Might be the right call for the wrong reason.  Did you have the ball before the runners foot contacted yours?  If you did, then runner out as you describe the play.  If the runner made contact with your foot prior to you having control of the ball, the call is dead ball, runner safe due to your obstruction.

The defense can not deny access to the runners chosen part of the base prior to the fielder at the base having possesion of the ball.