Select free weight exercises rather than machines whenever possible.
Exercise machines are great for some things like rehab, but they should be limited for healthy baseball pitchers.
Free weight exercises require the body to stabilize the joints, core, and balance the weights. Machines keep the movement fixed in a certain plane, but nothing is fixed in baseball—it's dynamic.
This means body weight squats, for example, are better than using a leg press machine to build lower body strength.
Remember, most pitching-specific movements are done with your weight on one leg or the other, so it's wise to include exercises like lunges to be able to develop functional strength and balance while on one leg. Or in your example core exercises standing with med balls for example rather than crunches on your back.
Hope this helps.