running out of base line

Question
the catcher missed the ball on a called third strike. the batter now begins to run to first to try to be safe but during the play the catchers throw to first strikes the base runner in the back. in this play the umpire called the runner out for interference. I doubt this is the right call. This call happened twice during one game against the same team. Was this the right call?

Answer
This is a valid call and it takes an umpire that knows the rules, is positioned correctly and paying complete attention to the game.

Running to first base, the batter/runner (BR) must be in the running lane to avoid interfering with the defense.  If any part of the BRs body is on or over fair territory and the ball thrown to first base hits them in the part of the body that is on or over fair territory the call is dead ball, BR out, runners return to base at time of pitch.

Some catchers are coached to only throw to first with a runner on third in a dropped 3K situation if they are sure they can hit the BR to draw the interference and return the runners to their bases.