This didn't precisely happen to me today, but it made me think of this hypothetical:
R1, outs don't matter. Ground ball to F4. F3 is a doofus standing in the wrong spot and obstructs R1. F4 charges the ball, and reaches it about the same time as R1, who (gently, non-maliciously) bumps into him. What've we got?
I had just the INT in a LL Majors game today...coach asked about the OBS, but I didn't see it as PU and my partner didn't call for anything either. So I said we didn't have that, coach said ok and we played on. But it got me thinking how to sort that out--my initial take is that the OBS doesn't absolve the runner of his responsibility to run the bases correctly, to include don't interfere with the fielder. But I'm curious. Arguably, if the obstruction was severe enough, he's past that point before he could interfere. But you could loop yourself in circles that way--is there an established precedence?