Jam,
What I would start with and further research is how to generate early momentum. As you can see from the picture below, you do not generate any forward momentum prior to or at hand break. In your case, you can see the lack of momentum (poor back leg drive) coupled with early hand break
Common tendencies you should avoid in this first phase of the pitching delivery
- Lack of early momentum and getting stuck over the back foot
- Leading with the shoulders
- Raising the throwing arm early is often the result of breaking the hands before weight shift
Keys for the beginning of your delivery that you need to further research and do lots of throwing drills and dry drills
- Early weight shift while getting gathered and loaded
- Proper use of the back leg drive foot to help generate ground force
- Lead with the hips
- Momentum towards home plate before hand break
- Stable and engaged with your back leg
- The core or center of gravity and hips lead the movement
The Wall drill may be a good place to start
Steve