Stabilizing the front leg is a key component in 3X Pitching and increasing velocity. If we do a great job building power and torque but we have lead knee flexion then all of our hard work is almost completely wasted. I get it, it is a big issue with low velocity pitchers and it is frustrating as hell. This is why I love watching Justin Verlander. He is the King of the lead knee and it is awesome when you see someone use it so effectively.

I have thought this through hundreds of thousands of times and here is the problem. Like you said, it isn't just one problem. There is a handful of issues that could be occurring and the more variables, the tougher it is to solve the equation. Here is a list of factors that can cause lead knee flexion.

Lead Knee Flexion Factors:

1. Poor Leg Strength (With hard throwers 175% of body weight hits front leg at front foot strike)
2. Poor hip rotation (At front foot strike, if hips are closed, it will put torque on knee as hips rotate open. You can actually see the lead knee rotating while it is flexing.)
3. Knee over heel (Once your front leg force vector goes vertical, it is very difficult to stabilize front knee.)
4. Poor hip mobility (The tighter the hips, the less mobility and stability in the leg)

If a pitcher is dealing with all 4 factors here which most young pitchers are then he will not only need to make mechanical adjustments but strength and speed gains and enhance mobility through stretching and soft tissue work.