Hitting
Wii Baseball isn't like other baseball games, where it's a true simulation of everything involved in the game. There's no fielding or base running (at least none that is under the player's control). There's only hitting and pitching.
Timing is everything: Once you learn to time the pitches correctly and swing at the right time, you'll find yourself becoming a much better hitter. This simply takes practice.
Use direction: In addition to timing the swing, the direction in which you swing can have a major impact on how the ball behaves. Swing up to send the ball flying. Swing down or directly level to hit more ground balls and line drives.
Watch the seams: If the seams on the baseball aren't moving, it's a splitter. Avoid swinging at these: nine times out of ten, this will be a ball.
Pitching
Pitching in Wii baseball is a cinch to learn but takes some time to master. Take the remote in hand and make a pitching motion. That's all there is to it...for the beginner. With these tips, you can take your pitching to a higher level, and confuse the opposing team.
The fastball is the default pitch. The harder you sling the remote, the faster the ball travels. Make sure you have your safety strap on!
To throw a curveball, hold down the B button as you throw.
The screwball is the opposite of the curveball. While the curveball curves from right to left, the screwball curves from left to right. Hold down the A button while throwing to accomplish this pitch.
To throw a splitter (which will count as a ball if the batter doesn't swing, but will almost surely be un-hittable if they do swing), hold down both the A and B button while throwing.
Advanced Pitching
Advanced techniques can help you become the Cy Young award winner of your household. Use the D-pad to change the aim on your pitches. Just before throwing, press in a direction on the pad (no need to hold it) and the pitch will head off in that direction. Also, to have a little fun with your batters, you can press 2 before your pitch. You'll feel the controller rumble slightly. Throw the ball...and your pitcher will throw it underhanded. Press 1 to return to normal overhand pitching.