Hope all is well. Sorry I couldn’t get back to you sooner but I got very busy here. A couple questions first. Is Evan throwing too high? Too low? Control problems? If he doesn’t exhibit any of these, then I would say this is his delivery. I am sure some will say he falls of to the side of the mound after his delivery, which he does. But you have to ask yourself, maybe he doesn’t have a problem at all. Maybe his mechanics are more rotational than what coaches or you are use to seeing.
However, I do see a possible reason why he falls off the mound to first base side after his pitch
-Falling off the mound is mainly caused by the pitchers eyes. If the eyes are not locked onto the target, that may be the reason why he is pulling his head out (look at the bill of Evan’s cap compared to the pitcher). So the next question is, why is he pulling his head out, it could be because of the eyes not locked onto the target, or it could be because of the placement of his pitching arm glove at ball release. If this is a concern for him, then I would start by having him focus on his eyes. That should take care of the head. But if he still falls off over to one side then I would not only focus on the eyes but also focus on the glove arm action. Take a look at the pics below
–Hit the spot drill: simple drill while playing catch or throwing bullpens. Partner holds the glove (target) as the pitcher work’s on focusing on this target with his eyes and hitting the target every time. Drill is about 60 feet away. Have him also start tucking his glove but please don’t compromise his rotation.
Hope this helps