This is a big issue and can be related to a different bigger issue unrelated to swinging the bat. I’m talking about lack of range of motion, especially in the hips and upper (thoracic) spine. With young players, their bodies are growing and they probably don’t pay too much attention to stretching. But a poor follow through can and will affect the way they swing the bat because they can’t physically get to the spot they need to consistently.

If a hitter is not able to fully get his hips through at contact, he will swing with mostly arms (see point 8 above and what that does to swing path when the hands get way out in front of the body). And if a hitter is not able to fully rotate his upper body after contact and separate the upper half from the lower half, one of two things will happen; either his swing will resemble more of a “gate” swing where his whole body will turn in unison and moving his feet all over the place or the swing will stop prematurely sacrificing power.

The points to look for are threefold: 

1. Good lower body rotation
2. Good upper body rotation
3. Proper finish with the hands.

Poor lower body rotation is evidenced by the back foot either remaining in place or flat on the ground. In either case, the back foot must be pointed at the pitcher and up on the toes for a good follow through. The hips will now be square to the pitcher. Upper body. Ensure the back shoulder is pointed at the pitcher at follow through. Lastly, make sure hands finish at or near front shoulder.

If you can get a hitter to start in the proper spot and end in the proper spot, chances are better that he can take a good swing. Get the hitter to focus on getting to the proper spot at follow through.

Quick Fix Drills

Lower Body Rotation

1. Step in and hit drill: Have the hitter step back off tee a step and off to about a 45 degree angle away from the plate. The hitter starts with the bat on the shoulder with feet together facing the tee. He then steps with back foot to where he normally stands in the box with the back foot and lifts the bat off his shoulder, then he strides into hitting position and swings. This gives him the feeling of getting off his back side, creating some momentum and driving his weight into his front side.
2. Dry swings with bat behind lower back and a proper hip turn to pitcher.

Upper Body Rotation

1. Have hitter hold follow through at end of swing and ensure back shoulder is pointing toward pitcher.

Hands

1. Hands need to finish right at or close to corner of front shoulder. You may have to over-emphasize this point. For instance, for a hitter that finishes way too high, have them finish on the side of their front arm. For a hitter that finishes too low, have them finish above their front shoulder. The over-emphasis may result in changing the follow through and getting your hitter to a better finishing spot with his hands.