Ideas for why velocity spiked and then went back down again

Just a little back knowledge. First year pitching for my son. He started year okay with basically stepping straight back towards 2nd (rocker step) to start windup and took the ball straight back out of his glove like throwing a football. He did ok with this. About have way thru year he started dropping his arm down after breaking his hands some to get a longer arm path. Again he did ok with this. About the same velocity and control. Then after a couple games of this he changed his rocker step so that he stepped more toward 1st base and dragged his right foot over the rubber and picked it up slightly and placed it in front and next to the rubber (and parrellel to it) to start his windup. Kind of how Roger Clemans and Nolan Ryan do it. I had him look down breifly to make sure his foot was next to rubber. Did this because he never seemed to consistently get his foot next to the rubber the old way and sometimes his foot would slip in the loose dirt in front of the rubber. Also just seemed to me of a more natural way to get his foot placed right and to get mommentum going toward home. The first game he did this he had noticeable more velocity and control. The second game even more. Seemed he was throwing much much harder. If I had not of seen it I would have not believed how hard he was throwing. Then the third game after about a week off, the velocity started to go back down and started missing high, but had pretty good control. Fourth game velocity was down again and did not have good control at all. I asked him what he is doing different and he does not know. I specifically asked him what he did different the games he was throwing so hard and he says he does not know and did not realize he was throwing so much harder. I watch his foot work as far as the rocker step and it seems to be the same as when he changed it to stepping more toward 1st base. Anybody have any ideas? Maybe he is exaggerating something he is doing more or less and realizing it. I am not sure how low he was dropping his arm after hand break during the games he threw so well because I was focused on his feet. I warmed him up before the game he threw so hard and I remember noticing not only how hard he was throwing but how fast he was rotating his shoulders when throwing. I thought to myself I never seen him look like that before and that looks tiring how fast he was unwinding his upper body and shoulders when throwing to me. I don’t ever remember seeing as much and fast rotation before. I told him several times to save some for the game, but when he went in he seemed to throw even harder. When I throw with him now it does not look like that.

I am totally dumbfounded and frustrated because now I know what he is capable of.