I often hear coaches and instructors tell their pitching students to "stay closed". I want to clear up exactly what "staying closed" as a pitcher means and how to use it to your advantage. The common myth is that pitchers open up by pulling too hard with their glove hand, causing their frontside to fly open. This could not be further from the truth. Staying closed has everything to do with a pitchers lower half and not the upper.
First, take a look at the pictures below. I picked out some of my favorite pitchers leading with their hip. The key to staying closed while driving down the mound is leading with your hip. When we lead with our hip, our front foot naturally gets down closer to our body. This means our stride will be shorter. When are our stride is shortened and we foot-strike inside of our center, it is easy to get out front of your head and drive the baseball. Driving down the mound leading with our hip helps us achieve a short powerful stride that allows us to get over our frontside. When we consistently throw the baseball in front of our head, we eliminate the vast majority of slowly developing arm injuries.
Pitchers who "open up" too early are simply leading with their feet. When we lead with our feet instead of our hip, we naturally will fly open and our arm will drag through the zone. Our front hip opens up too early, causing the arm drag. When our arm drags, we miss to our arm side of home plate. Take another look at the correct way to lead with your hip in the pictures below.
Take a look at Lincecum below. He is a great example of incorrectly leading with the feet. You can see in the pictures below that his front foot is leading his stride, not his hip. This will cause his arm to drag because he is outside of his center of gravity. Lincecum cannot get out over his frontside to drive the ball because of the long stride which starts with him leading with his feet. His arm has too much catching up to do and he will usually release the baseball behind his head and push the baseball. The mechanical changes he should make start with leading with his hip more to stay closed and get his foot down sooner.
The next change Lincecum should make involves tightening up his hands, but that is for a different article.
Ventura and Hernandez are two of my favorite RHP's. They both stay closed a long time by leading down the mound with their hip. In both cases, Ventura and Hernandez are almost leading with their left butt-cheek. Another reason we want to stay closed is to avoid arm problems and missed locations. Later in this article I will get into the details of how arm problems can develop by leading with your feet.
The longer we stay closed, the more rotational torque we build with hip to shoulder separation. Everything in baseball is rotational, and pitching is no exception. By leading with our hip, we are essentially cocking our hips, or loading them like a hitter would do.
Pitchers who consciously lead down the mound with their hips will throw harder because of more rotational torque and a foot-strike that lands within their center, allowing them to drive the baseball with downward tilt in front of their head.
Pitchers who incorrectly lead with their feet (Lincecum) will miss arm side because of something called arm-drag. Arm-drag is simply when a pitchers arm does not catch up and the pitcher gets heavy (or feels the weight of the ball) behind his head. When arm-drag occurs, the baseball is released too soon or "pushed". Arm-dragis a lot like wear and tear on your car. Arm drag will cause serious stress on the pitchers shoulder and UCL (ulnar collateral ligament). When we lead with our hip, our arm will always catch up and we will be able to deliver the baseball in front of our head (driven pitch).
Next time you hear your coach say "your opening up" or "stay closed", tell yourself to lead with your hip.