When you say that you do overhead squats, are you doing the snatch in your routine?
I have had a recent infatuation with the front squat. I can't use as much weight as a normal squat, but I get a better workout because it's harder to cheat on a front squat than a regular squat. "Cheat" meaning leaning forward too much and maybe not going all the way down. If you lean forward too much on a front squat, it's tough keeping the weight in place.
My basic routine is to do a clean, and then go directly into a full front squat, and that will be one rep. Right now, I'm using 185 pounds (someday, kilos). I try to keep the reps low in my sets.
One guy at my gym does multiple reps of hang cleans, which I think would make the most sense if you are doing higher multiple reps of cleans.
I find it breaks rhythm when I try to do multiple reps of power cleans because I have to wait for the weights (no pun intended) to stop bouncing after I put them down.
If you don't want to do the front squat in conjunction with the clean, you could try lunges. Or also try doing cleans with dumbells. After your set of cleans, do a couple vertical jumps or other plyometric exercises. Do a power clean, and then do a hang clean, and then a front squat.
Since you're a pitcher, any combination of those with the clean should help you build a strong base to push off the mound.
Those are just some ideas.