Having a strong, active core for both throwing and hitting a baseball is essential and it can be the biggest factor in improving overall performance.
Everything starts and ends with the core. I weak, undeveloped core will be a detriment to other areas and aspects that a player might be working on or trying to improve. Without proper core work, the rest is just going to not work well or develop the way it should.
Training the core for baseball can be done in various ways. Below I have included some videos.
Check them out and give them a try.