I know I keep repeating myself but that’s only because it is so important. Whether pitcher or hitter, the biggest source of power for a baseball player is the hips.
Check out this video clip of Babe Ruth. Everything about this swing is powerful.
He leads with his butt creating a powerful position with his knees inside of his feet as he strides. As soon as his foot touches, his front leg becomes a wall and his hips fire. Notice how quick his back knee comes forward (the knee is indicative of his hip turn as it can’t move forward in this position without the firing of the hips). As his hips fire, his top half stays back a split second creating the coil that then drives his hands at the ball as he unravels. During all of this, his front knee contracts, which sends all the hip energy upward and also allows for maximum range of motion.
Notice how the above description could have been about a pitcher. Next time you throw, try to recreate what you’ve seen.