[UmpTTS43]

According to the NCAA, the correct answer is A. Since F2 had to leave his initial position to go after the ball, he lost his protection from committing OBS. The NCAA, as well as OBR, defines "in the act of fielding" if the ball is "near enough" and "directly toward" the fielder. Since F2 had to chase after the errant throw, the ball was not directly to F2, therefore he was not "in the act of fielding" and that result ends up being OBS.

In situations where F2 has to go up the line to receive a throw, you have to judge whether F2 is chasing after the throw or has reestablished a position in order to receive the throw. If F2 has gone up the line and has stopped or gained a position to where the throw is "directly toward" him, you can now consider him "in the act of fielding." If F2 is still chasing, as in the OP, he has not reestablished his position.