Too super super subs

I was forced to bring a striker from my youth squad up to the first team due to injury. He's 16 years old. I bring him on as a sub around the 65th minute. He scores twice. I think, wow, that was a total fluke. I don't think much of it.

A couple games later, I sub him again around the 65th minute. He scores a hat trick. Ok, that's really weird. I decide to start him. He gets a 5 rating and does absolutely nothing in the next three games.

I go back to subbing him for the next dozen games or so. He now has 14 goals. What gives?

16 years old. Perhaps the thought of starting scares him? Too much pressure. Perhaps mid game your team is playing better and it helps him, the oppo may be tired etc etc.

maybe his stamina or smth doesnt allow him to play good for 90mins. or pressure as nepenthez said

my supersub is dentinho. also never plays good when starts the game

whats his name? is he a regen

There are some players of mine who are the exact opposite, I don't sub some on because they only perform if they're there from the start.

What was the score when you brought him on? As a 16 year old I imagine it would be a lot easier to come on and slot into a team that are already 2-0 up than be asked to start the game and play a part in putting his team in that winning position in the first place.

Or maybe if you were losing when you brought him on he had the whole "no fear cos he's a kid" attitude going on for a cameo appearance?