Coaching a certain feel to a swing is often discussed with talented players at higher baseball levels. However these conversations can often be tough to coach and discuss, in order for players to understand. When a baseball is coming towards a hitter there are a couple of factors at play.
The feel of the swing to the hitter himself, the thought process as the pitcher gets set, and what the hitter actually looked like or the reaction to the baseball. So yes the more athletic you are and more in shape you are the better reaction you will have, but there are also great hitters with just excellent reaction, causing a smooth bat path.
The idea of coaching this predicament is to show a hitter a drill that produces the correct feel of a successful reaction or swing and start there. Sometimes strictly discussion is tough for a hitter to connect to the actual movement or feel he is trying to create, so a drill is important to connect the two.
Then discuss the hitters thought process as the pitcher starts his windup that will properly connect to the feel he was just creating with the drill. If the thought process produces the same feel as the drill and a positive result from the swing continue to practice to master that feel and thought process. Mix the drill in with front toss, and keep the hitter focused on the thought process that creates the feel and results in a correct bat path.