[mbyron]

A collision by itself tells you nothing. True, fielders are protected on a batted ball. But the OP does not tell us enough. For example:

Case 1: Looping line drive in the hole, 10 feet over F5's head. R2 is running on the pitch. F5 leaps in vain for the ball and comes down in R2's path, where they collide. Ruling: F5 could not have fielded the batted ball, and thus could not have been interfered with. This is obstruction: if, in the umpires judgment, R2 could have scored on the play, award home.

Case 2: Bloop in the gap behind F5 who is playing in, R2 running on the pitch. As F5 moves back to field the batted ball, he collides with R2. Ruling: Interference. Dead ball, R2 out, BR awarded 1B (if less than 2 outs), other runners return unless forced to advance by the award to BR.

Case 3: Hard line drive to LF. R2 steps back to 2B in case the ball is caught, but it gets through. He then takes off to 3B as F7 fields the ball. The throw to F5 is off line and pulls him off the bag into the infield, where he collides with R2, but fails to apply the tag before R2 reaches the base. Ruling: this is nothing, R2 safe, play on.