This pitcher has much work to do. Chris is right about the low elbow coming through. It should be at shoulder height. He's also right about the lack of hip/shoulder separation at landing. This is mianly because, at front foot plant, his shoulders have already squared to the plate. Much, much, much too early! The shoulders should be aligned with a straight line between home and second at this point and the hips should be open to whatever degree his body allows.
Also, he has no forward trunk flexion into release. When that front foot lands, the shoulders then, not earlier, rotate around the spine while the elbow starts forward and the chest is thrust forward. Then, into and beyond release, the trunk must flex forward and on to a "flat back finish" over the front leg. The rotation of the shoulders continues past release also, as the trunk is flexing forward.
There are timing issues here that need work but these fundamental things must be addressed. Has he always had these mechanics?