Help with the stride

Hi, I’m 15 years old and lately I’ve been looking to make my pitching motion a better one so I can gain some velocity and I know theres a lot of tips on that, I’ve read them various times but don’t quite know if I’m in the right way of making my motion better. So, the problem is during my stride. I read the article with Roy Halladay : Where pitchers’ power comes from. I’ve recognized my flaw and it’s that I lead with my knee instead of my foot. But what I don’t get is : Do whe have to keep our hips closed the longer possible sothe hip rotation is quicker? Because I’ve tried to stay closed as long as possible but it really feels unconfortable and felt a little backpain when I landed. Or is simply leading with the front foot going to make my hips turn faster and give me more power?

I was always taught to lead with the hips when striding. And don’t keep closed as long as possible. When your foot lands open your hips and wait a bit to turn your shoulders. But I’m no mech expert.

Great example of what to shoot for.