Rundown Obstruction?

[tzme415]

Well things have settled down after the holidays and I am going through my notebook from last year, while waiting for the new softball season to begin. I have a few situations from last year that I would like to get some input on and this is the first:

ASA SP Adult Men - R1 on 2nd, R2 on 1st 2 out - Batter hits a ground ball to left - R1 rounds 3rd, R2 rounds 2nd - Ball is thrown into 3rd, R2 gets caught in rundown so R1 scores - BR stops at 1st - Here is the part that causes a question - F5 chases R2 toward 2nd then tosses ball to F4, R2 starts back to 3rd, F4 tries to tag but misses starts to chase but is slower than R2 so tosses to F1 who is near 3rd, F4s momentum carries him toward R2 as R2 turns back toward 2nd and runs into F4, F1 tags R2 for the out. R2 of course wants obstruction, I don't call it because I don't think F4 had a chance to avoid R2. I know this may be a HTBT thing, but who is responsible to avoid the contact there and what guideline do you use to determine if this should have been obstruction?

Thanks for your input.