Generally speaking, when you’re trying to hit a baseball, you need to turn and lead with your hips, but that doesn’t work on an inside pitch. Why not? For starters, if you open up your hips and lead with them, then you’re going to make contact with the ball too far out in front, which means you’re going to yank it foul. But this isn’t an instructional, necessarily; it’s how guys do it in the bigs. If you watch Anthony Rizzo or Carlos Correa, you’ll notice them start their swing, but once they realize that the pitch is burying inside on them, you’ll notice their arm starts to pull inward, instead of extending outward like you would on a pitch down the middle, or on the outer half. Because of this, you lead with your hands. You’ll find that your hips are placed about halfway in between your starting point and your normal ending point. This way your hands are in front, which effectively allows you to barrel up the ball, and to keep it fair instead of pulling way foul.
Example of Prince Fielder utilizing this method with the Detroit Tigers (Courtesy of MLB.com):