Many of the pitchers that I work with are High School and collegiate level athletes. I also teach my share of youth athletes. When I teach students that are younger than their teen years, stride length becomes an issue. Here is what I mean.
When a pitcher has great core strength and they have matured into their bodies, they can get away with a very long stride. In fact, you have heard this from me before that a stride should be at least 100% of your height. This is great because most pitchers generate more momentum, in turn they get more pop on the ball. When a pitcher takes such a long stride it is imperative that their hips rotate before their upper body; this is referred to as delayed shoulder rotation.
When you delay your shoulder and begin to rotate your hips, you activate your core. If you don’t use your core to throw the ball you are missing out on using your entire body to throw the ball. That’s the point of pitching mechanics; using your legs and hips for that power. You don’t just rely on throwing with your arm.
When I teach younger athletes I have to instruct them a couple of times to see how long their stride should be at their level of development (notice how I didn’t say age; Age has nothing to do with when a pitcher should throw off-speed pitches etc.) Some young pitchers cannot rotate their hips correctly with a longer stride and be effective. To enable them to do that, sometimes it is necessary to shorten their stride by a few inches; not too much. Doing this will help some pitchers rotate much better to release of the ball. See, young pitchers have not developed sufficient core strength to throw with a long enough stride. They can’t rotate their hips all the way around and they end up leaning into the pitch instead of rotating around into it.
The good news for you coaches teaching youth athletes how to pitch; most young pitchers don’t take a long enough stride to worry about shortening it. You will have to encourage these students to gradually lengthen their stride while maintaining great hip rotation.