As the dad of a kid who just finished his D1 career, 3 years of it as a pitcher....it's blocking, no question. If a pitcher can feel comfortable throwing any pitch in any count and a guy on third, he can be almost untouchable. If he's afraid to throw a curve because he might bounce it and he knows his C can't handle it, he's not going to be nearly as effective. You can't pitch being scared that your catcher can't handle what you throw him.