Should I be concerned? Or is it just my son finding himself?
I have a few videos of him pitching. The first one is from the Fall of last year. The other two are from last week. His mechanics have changed and I’m not sure if its for the best. He tells me he feels like he’s throwing harder then ever and has reached 77mph but sits around 75ish. He turned 15 in December and is 5’7” 160lbs.
In my opinion, he’s in the process of finding himself. At fifteen he’s still going through puberty and has a couple of growth spurts coming, so don’t rush things, and don’t worry. Every kid has his own pace.
And at his age he’s probably thinking of experimenting with a curveball or some other breaking pitch, and I wouldn’t be surprised if he’s already starting to work with one. Let him find his own path. 
In my opinion, I like the first video better than the last 2. In those 2, he’s lost any forward trunk flexion contribution he had and, as a result, he’s standing up very straight as he releases the ball. Notice his finish in each. His stride may even have gotten shorter. So, now he has a short stride, with no trunk flexion. He’s probably just trying things out and that’s part of the gig but I’d feel better if he put those items back to work.
Agree with Zita and DM, Might be in the process of experimenting with different things and finding himself.
I do like the mechanics in the first video. He appears to have more intent and momentum to the plate.
Thanks guys, and gals
I kind of liked the mechanics in the first vid my self but I don‘t want to say something to him that could put doubt in his head since he has been pitching very well. I would like him to not be so up right when he finishes, and he said that was one thing he felt was wrong. I do know that the ball seems to be not only jumping out of his hand but under more control with good movement. When he throws his fast ball I sometime find myself making last minute adjustment just to catch it(but I’m also getting old). His curve has a more 12 to 6 then his more slervey like pitch he had previous. Again that could also be from him growing I guess. He did say he felt like he had more control over his body as a whole. So I’m going to see if I can get him to finish a little better and maybe tweak his stride.
I really appreciate the time.