(1) He needs to move forward faster through knee lift and stride into foot plant. This will help in a number of ways: will give him better timing, will help him be more consistent, should help him throw a little harder.
(2) He need to control his glove better. The initial extension of the glove arm out front to an “opposite & equal” position with the throwing arm is good. But, from there, he drops the glove to the side. That risks pulling his posture to the side, pulling the shoulders open early, and leaves him in a position that is difficult to protect himself from a come-backer. Once the glove is out front, he should turn it over and stabilize it somewhere in front of his torso. Doing (1) above will make this easier.