Complex sentence: A "modified" fast pitch is identical to a "windmill" pitch except the arm is not brought over the head in a full windmill motion, but instead is brought behind the body and is then thrust directly foward for the release.
Split into simpler sentences: A "modified" fast pitch is identical to a "windmill" pitch except the arm is not brought over the head in a full windmill motion. In a "modified" fast pitch, the arm is brought behind the body and back in front for the release.