With this question, the initial energy is actually generated in the lower extremities and then passed, in a series of steps, up through the body and eventually into the baseball. In other words, in order for the baseball to get its kinetic energy, the pitcher must begin generating that energy in the lower extremities and then "move it" up the body, to the arm, and eventually into the baseball. Thus, the efficiency at each step must be taken into account. Since the legs aren't really throwing the baseball (just directing energy into the arm, so to speak), we need to include the efficiency of the upper extremities, too.If the question is only asking about the energy of the lower extremities why do you multiply the effeciency of the upper extremities as well?
I hope this helps!