Interference or Incidental Contact?

Question
F4 playing deep, R1 on first.  BR hits a slow ground ball.  F4 charges in and collides with R1 with both in motion.   I called it incidental contact since in my judgment, both fielder and runner were in motion and just collided.   The other umpire said I should have called interference.  Who's right?

Answer
Hi Lenny,

If F4 was hindered from attempting to execute a play as it seems they were just from your brief facts, I would have interference.  A runner must vacate or not enter any space necessary for the defense to field a batted ball, just because one or both are in motion means nothing.

As usual the caveat is I would like to see it.

Mark