Research suggests that power is very plane specific. Meaning just because you have a 40 inch vert or run a 6.5 60 yard dash does not mean you are going to throw 90 MPH.
All the deadlifts, squat variations, presses, rows, and carries are great, but at some point a pitcher has to train outside of the sagittal plane. A large portion of a pitcher's strength training program should take place in the frontal planes and transverse planes.
Lateral Strength exercises, rotational med ball throws, and lateral jumping drills are a must have in any pitcher's training program.
Try these exercises to increase your strength and power outside of the sagittal plane:
Make sure to sit back into the hips, keep the chest up and the knee should be slightly inside of the foot. These are also great from a mobility standpoint because they will force the athlete to lengthen the adductors on the opposite side.
Step Behind Side Toss
The step behind is a great way to learn how to load into the back hip. From there you want to snap your hips through as hard as you can making sure you are getting full hip extension.
This is an awesome exercise to teach athletes to get extension off of the front leg. I tell our athletes to think of this as a full body exercise from the ground up, and I really hammer home to drive off that front leg.
Lateral Sled Drags
I love this exercise because you can load it up pretty heavy, and it is a great single leg and lateral strength developer. It is important to squeeze it tight to stabilize the shoulder and stay low to drive into the ground, rather than just side-shuffling along.
Drop to Lateral Bound
This is a more advanced variation of a lateral bound. If you do not have adequate strength or technique you should stick to standard lateral bounds until strength improves.
The initial drop off the box enhances the stretch-shortening cycle (a process that occurs in your muscles to create power) by teaching the athlete to absorb the force of the landing and then immediately exploding into a lateral bound.