This is a great exercise for softball players because it helps to increase not just their core strength, but overall strength, as it targets muscles in every part of the body. If you are doing this exercise for the first time, start with some lighter medicine ball, and as you get stronger, gradually increase the weight.
To do medicine ball squat to slams:
Start in a squat position, placing your feet just a bit wider than your hips, and hold the medicine ball with both hands under your chin. Now extend up, bringing both your hips and toes up, along with the medicine ball. When the ball is in the highest position, slam it down. Do 3 sets of 10 reps.