In which situation is the force applied to a baseball the greatest? A. As the pitcher is winding up to throw it B. As it is being thrown...

Without actually testing the forces being applied, we have to generalize and assume a few things; for example, it's safe to say that the question is asking about the forces acting on the baseball along a vector that will propel it towards its target. If we were being more thorough, we would have to acknowledge that multiple force vectors are acting on the ball during the windup, and these combined vectors may actually result in a great amount of applied force(s) during the windup than the release. However, without knowing all of the mechanisms of action taking place during the windup, this is speculation. We should focus instead on the target-vectored force, which means the answer is B.

We can be pretty assured that, if the pitcher released the ball at some time during the windup (answer A) then the ball would not be released with anywhere near the velocity that it does when released at B. This is how we know that a greater force is being applied. We also know that the force being applied between times A and B is increasing, basically because the pitcher's arm has to "catch up" with the ball in order to continue propelling it forward, otherwise the ball would leave the pitcher's hand prematurely.