Basically, his problem was how he was gripping his old change up- his grip was causing him a lot of pain. So, what the coaches did was change the grip of his change-up, but of course in doing that, he has to learn how to "feel" that pitch throw it effectively. So, that's the issue with Routt right now.
Pitching is all about feel- in other words, being comfortable with how you are throwing your pitches to the point where you can control them. That's why it takes pitchers a year or so to learn how to throw a pitch effecitively a lot of times- even in the pros.
You have a few types of change-ups- I think most pitchers throw a circle change-up that Tom Glavine made popular where you grip the ball with your middle and ring finger and your index finger and thumb come together to make a circle.
Another kind is what my Dad used to call a choke change-up, but I think most people call it a three-finger change-up where you basically hold the ball in the back of your hand with your index, middle, and ring fingers across the seams and your thumb and little fingers are at the bottom. I think this is the kind that Trevor Hoffman used to throw.
Glavine's change-up seemed to cut a little more, but Hoffman's seemed to have a little more sink on it- I don't know if that's typical for both of the types of change-ups. But basically, by holding it in the back of your hand- either grip- the friction from the fingers will slow the ball down so that the pitcher can keep the same arm motion as a fastball- which adds deception to the hitter, and the sinking action make it tough to barrel up on the ball- it's a great pitch to throw if you need a ground ball.
I know that's more than you asked for, but I was on a roll.