Heavy weight, heavy grip work, below are some good forearm work for baseball, helps with bat grip and bat speed, may be a good start for you.
Farmer's Walk
Use proper form: a solid grip with fingers securely fastened around weights, core tight and shoulder blades pulled down and back.
- Start with heavy dumbbells
- Hold dumbbell in each hand
- Keep arms straight next to sides
- Walk in straight line and maintain good posture
- Keep core muscles tight
Sets/Duration: 4x30 seconds
Wrist Extension
- Sit on bench with elbows resting over inner thigh and palm facing down
- Holding light dumbbell, extend wrist up
- Return to neutral position; repeat
Sets/Reps: 4x15
Wrist Flexion
- Sit on bench with elbows resting over inner thigh and palms facing down
- Holding light dumbbell, flex wrist up and down
- Return to neutral position; repeat
Sets/Reps: 4x15
Hammer Curls
Pronating your arms engages the forearms to help the biceps work through the movement.
- Hold dumbbells at sides with palms facing in and thumbs up
- Flexing the elbow, curl dumbbells to shoulders, keeping palms facing in and thumbs up through whole motion
- With control, lower dumbbells back to side of the body
Sets/Reps: 4x12
Bicep Curl/Eccentric Pronated Curls
- Perform Bicep Curl with palms facing out
- At top of movement, pronate forearms so palms face away from body
- Slowly lower dumbbells back to start position
Sets/Reps: 4x12
Rice Dig
If your coach has a bucket of dry rice in the dugout, you can do this classic baseball forearm exercise during practice.
- Sit on chair and place hand in bucket filled with rice
- Dig through rice using forearms, wrists and fingers
Sets/Duration: 4x60 seconds