Use Power Swings Sparingly
The four different types of swings you can initiate in MLB The Show 21 are standard, contact, power, and bunt and whenever your best hitter makes an appearance at the plate you will feel inclined to use your power swing as much as possible in order to hit the ball out of the park. This is something you should resist doing as using power swings by default will lead to you regularly missing the ball. To have success with the power swing you need to bide your time and only use it when you know exactly where the pitcher is going to put the ball in the strike zone. The rest of the time you should stick to standard swings.