When coaches improve player's mechanics, if they just do it with only their experience, feeling and imagination, it won't work out. It might work, but it doesn't in most cases.

As some body segment affects other segment's motion through joint using muscle and bones, there's a reason or cause that the mechanics becomes like that.

Coaches need to have an ability to have an insight of root cause as well as knowledge of physics and anatomy.

When patients come see a doctor, the doctor can tell the method/process how to cure the disease/symptom, and prescribe medicine precisely. However, there's a case in which the disease gets worse or doesn't heal at all, because the doctor has never fixed it up and he managed to prescribe it with doctor's pride. It goes same way for coaches. You need to find the cause of problem and can see the process of how and where you fix to resolve the problems. If you just chage the motion without any grounds, you will train player in improper way and the player's performance wouldn't get better or it would lead to that the player keeps getting injured.

If you don't understand properly about physics and body on mechanics, you can't improve all players mechanics. That is, as you transfer energy to ball eventually in pitching/batting, it is important that the way of generating and transfering energy where and how generates power, how transfers it. Even if you are just ex-professionals or played for top-notch team, you can't fix the motion dramatically. Also, as there are so many misunderstandings in baseball such as "Stand properly on back leg", "Shooto is bad", "Top", "Hip First", "Swing your arm", "Push with your back hand", it happens that player's performance doesn't get better even if you change the motion. The true technical coach is who can change any players' mechanics.