Explosive movements are very important to incorporate into your training. Some good ones I like are MB jump squats, MB squats and broad jump, MB chop squat explodes(you do a squat with mb, let it touch the ground then explode up throwing the mb as high as you can into the air), MB full circle OH slams(w/full pitching windup and arm circle). Box jumps are good too.
I also have a large tractor tire and do plenty of tire flips either w/ both legs or single leg flips. This does a great job of working your core, hammys, butt and pretty much your entire body and really improves your explosiveness.
Running sprints are also a great way to become explosive. Short sprints of 10, 20 and 30 yards work great. 20 m shuttles work nice (set up 3 cones, each one 5 yds apart-start in the middle, sprint to one end, then the next end and then back throught the middle).
Basically as a pitcher you want to become a great athlete and be able to move your body explosivley down the hill. So any thing that improves your athleticism, while staying injury free is a great excersise.