I believe this would be under the new rule change(NFHS) and B would be given the ball and also able to run the baseline if that is where the ball should be inbounded(spot nearest where the foul occured).

This is assuming that I am correct in that the throw-in would not end until it has touched a player in bounds.

*I don't have my rule book with me so if I am mistaken someone please correct me.