The best way exercises will help you as a baseball player, is to help you prevent injury.
Because baseball has a lot of stops and starts, and sudden movements, it is important to practice a proper warm-up and mobility drills before jumping into nine innings.
I have compiled a list of exercises that will help you improve your baseball game:
1. Internal and external rotation
Start by grabbing a rubber band and tie it to a pole. Standing elbow height keeping your elbow at 90 degrees and touching your hip, Pull the band towards your belly button 15 times ( this is internal rotation). Do this without letting your elbow come away from your body. Once you have completed your 15 reps, now do the same thing, but pull your hand away from your body (external rotation).
2. Sumo wall sit
Because most of the game you are on the field waiting for the ball to be put in play, you need to be in the ready position. Practicing your sumo wall sits will help you build the quad stamina to be prepared for anything. Start by sitting with your legs wide, 90 degrees to the wall, lean on the wall and push your lower back into the wall behind you. Hold for 30 seconds at a time, making your way up to 2 minutes.
3. Wind sprints: 90 feet
Running from base to base is one of hardest things the body has to endure in baseball; going from a cold stand-still to a full out sprint is a recipe for disaster. Getting the body used to this task will help avoid injury. Start by measuring out 90 feet and set up a marker. Practice leaning with your foot on the marker and run from one marker to the other going about 10% of your full capability. Warm up like this for 5 or 6 times, and increase by increments of 10% until you are running 80-90% of your potential.