Timing and Movement Patterns (mechanics) is something that gets confused regularly. A players job is to make the barrel of the bat hit the ball. In order to do this they will always change their swing based on if they are late or if they are early.
This is why you should never work on one while doing the other. Timing is about feel. Like a dance. The closer you match the beat the better your swing gets.
Movement Patterns should always be developed with a still ball on a tee. The problem we always see is the set up of the tee is usually wrong for that individual. They actually are placing the ball to high or to low and early or late in the swing. Then the tee work won't transfer to the field. If you train to be late you can not hit the outside pitch. If you train to be early you won't hit the inside pitch.
You must train your movement pattern to be neutral. To do this hold the baseball by your side. Walk up to the tee and adjust it to that height. This is your neutral height. Everyone is different. Then check your stride foot. The ball should be lined up with it after strike. Now you have a neutral height and a neutral distance from the ball and its time to train your movement pattern.
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