[greymule]

Well, 8-7-J-5 gives the general case:

[The runner is out] when the runner interferes intentionally with any defensive player having the opportunity to make an out with the deflected batted ball.
[My italics.]

The case book (8.8.42) adds a little help in judging "intentional":

R1 on 3B and R2 on 2B when B3 hits a ball to F5. The ball goes off F5's glove and F6 tries to field the ball when R2 collides with F6. (a) As R2 tried to alter his path or (b) collides with F6 after having the opportunity to avoid F6 and make no attempt to avoid contact.

Ruling: (a) Live Ball, no interference. (b) R2's actions are judged to be intentional. Dead ball, R2 is out, R1 returns to 3B, B3 awarded 1B.

[Mistakes in grammar, punctuation, capitalization, and parallelism are in the original.]

It seems to me that "didn't have a chance to alter his path and avoid the fielder" would also qualify as unintentional.