When do you call interference?

[greymule]

ASA. R1 on 2B, ground ball to F6. R1 bumps into F6 as F6 attempts to field the ball. That's interference.

But if F6 has already fielded the ball, do you call interference on unintentional contact by R1? If so, is your criterion different from what it is if the fielder is in the act of fielding?

Fed interpeter in NJ says baseball or softball, runner interferes with the play, call interference. But that's Fed, not ASA.

Different game, of course, but in MLB I've seen R1 steamroll F6 after he fielded the ball, with nothing called (not even a tag out in the tangle).