12 YO RH Slidestep!

This is slow mo of my son pitching from the Slide step!

Nothing wrong with that. Yankee ace Allie Reynolds used to pitch from the slide-step all the time, because it actually gave him more speed in his delivery. I myself did the same thing; not only did it give me more speed, such as it was (I wasn’t particularly fast), but also better control and it enabled me to finish in a good fielding position. So if Junior likes doing it and it works for him, by all means let him stay with it and don’t try to change his motion.
What is more, when a pitcher throws from the slide-step it places base runners at a distinct disadvantage because they can’t get a good lead off him—they never know when a pickoff attempt may come!

He throws from the stretch as well! This is just to mess with the hitters timing,and like you said,helps keep runners honest.
He is much faster to the plate from the slide step!

Get him to relax his elbows by his side before he starts - holding them up creates too much tension in the arms; better to have them loose and relaxed. Once he starts, he should bring his hands down and break around the belly-button so he can have a nice pendulum-like movement with his throwing arm. Right now, he just gets his arm up into the high-cocked position and it gets there WAY too early; it’s just hanging there, waiting for his body to catch up.

Looks good at the beginning - leading with hips, however his shoulders catch up with his hips about halfway through his stride and by the time he has finished his stride he is already opening up his shoulders and has started his release. This causes him to start his shoulder turn even before the hips have a chance to fully rotate. Shoulder turn should not happen until after stride foot has landed and the back hip has begun to open. Once he gets his timing down he looks like he should be able to really bring it.

This is the ultimate flaw for him,and is proving the hardest to fix!!!
Upon any change to what you see with his back arm,comes intense elbow pain!!!
Any ideas???

look up Tom House’s rocker drill. this is a good drill that works on a pitchers timing from hand break to stride. It gives them a good idea of where the throwing arm should be in relation to what the hips are doing.

OC is right. Look up the rocker drill. He needs more glove side control to keep the shoulders closed off longer. He seem to bring his glove to his chest way too soon. He should actually leave the glove out front and bring his chest to the glove.

The rocker drill will definitely help.

Maybe you could post a video (real time and slow-mo, if possible) of him pitching in the manner in which causes the arm pain. It would be interesting to see what he is doing there.

Here is reg. speed of same video. Will try to get some more video at our next practice. I am tired of all the Snow!!! Spring is here its Baseball time!!!