If you made the argument that the coach assisted the runner in this situation, you would be entirely backed up by the rules. However, you would also be backed up by not calling it. It is entirely up to the judgment of the umpire whether the physical contact actually assisted the runner in advancing or returning. While contact is a prerequisite, contact, in itself, does not constitute interference. At umpire school we teach to use "In my judgment..." as often as possible before explaining your decision (of course, as long as it is a judgment decision).
