Yamamoto needs to learn how to protect himself better. Two hands on the stick at all times unless he's pokechecking. If someone's coming at him head to head, he needs to get his stick up to protect himself. Not once in a while, every single time. The only time he should ever back off from carrying his stick high is if he starts to accumulate too many penalty minutes.
If a defenceman is coming to rub him out along the wall, that butt end needs to flash up if just for show to make that player think about the last time he took a butt end in the jaw. Use his momentum to drill someone hard in the arms or torso.
If Yamamoto hears someone coming from behind... stick up, those hockey gloves need to hit the glass, like he's bench pressing, so his head doesn't hit the plexi so hard. Or he needs to go low more often and use his lower center of gravity to his advantage... and the big guy goes heavy into the boards. Go low in the open ice and the big guy flies ass over tea kettle.
The big guys will always target the little guys. Little guys needs to learn to reverse check and know how to do it so it hurts. Yamamoto should use his hips and butt like a weapon and learn to make the lower center of gravity work for him. Some of the best checkers ever have been shorter guys... because they understood and used physics.
Dekeyser completely punked Yamamoto in the preseason. Yamamoto got his bell rung and his teeth loosened. Cranked his neck or got a concussion... maybe hurt his shoulder. Yamamoto played in the WHL and not US college hockey, all this should be second nature to him.
For all Yamamoto's shortcomings the one that bugs me the most, it does not appear he hits the weights hard. His legs need to be thick like a speed skaters (he might even improve his skating) and his core needs to be ridiculously built up. Huge arms and a strong neck will always protect his head. You hope he can add weight in the right places that doesn't make him slow and increases his body mass and strength. He spent an entire summer working on his shot, where did that get him?
If Yamamoto wants to make an impact in the NHL he has to work his way so the first thing you think of when you hear his name is nasty little ######.