Obstruction or not?

[Jim Porter]

Originally posted by Mark T. DeNucci, Sr.
R1 on first base. Cather takes pitch and throws to F3 in attempt to pick-off R1. R1 breaks for second base. F3 then throws to F4 who is covering second base. As F3's throw gets close to second base, F6 jumps in front of F4 and catches F3's throw and tags R1 who is sliding into second base. R1 is unable to tag second base before being tagged by F6 because F4 standing directly in front of second base in anticipation of catching F3's throw.

Yes, that's obstruction. Only one fielder can be in the act of fielding the throw. That was F6 since he, in fact, fielded the throw. F4, therefore, is guilty of obstruction.