[lawump]

Under OBR intepretations, a fielder does NOT need to immediately "disappear" after attempting to field a thrown ball (as opposed to a batted ball).

From J/R:

"A fielder's "try to field" a thrown ball is a similar concept to a 'try to field' a batted ball, excepting that a 'try to field' a thrown ball includes the actual possession of the thrown ball, and the fielder's actions immediately after a miss or deflection of the ball. Therefore, a protected fielder on a thrown ball need not 'disappear' after deflecting or missing a thrown ball, and if fielder-runner contact is instantaneous, there is not obstruction. (emphasis added).

Thus, in order to answer the OP's question I think one would have had to have been there and seen the play described. If the collision occured immediately as F3 returned to the ground after jumping for the ball, then I would not have called obstruction but rather would have adjudged it to be a "train wreck". However, if the throw to F3 was so high, that F3 didn't even make an attempt to catch it (by jumping, etc.) but rather just stood there and watched it sail by, then I'd have obstruction, as F3 was never in the act of fielding the thrown ball.

My post is limited to OBR and does not include any refrence to Fed rules.