It is essential to train proximal lower extremity and trunk stability/strength. Without this, you're exposing your shoulder and elbow to some serious forces as a compensation to produce power. An article by Oliver et al. 2016 said it best, "Functionally training the body for UE performance, such as throwing, requires the LE to function efficiently in both double and single leg support. The ability to generate and transfer force from the lower to the upper extremity in single leg support is fundamental for all overhead activities."
The authors discovered the 'airplane' exercise exhibited moderate to strong activation of the biceps femoris of the hamstrings and the gluteus medius for lumbopelvic-stability. We also know T's and Y's exhibit scapular stabilization. Thus we give you the Modified Airplane. Quoting the authors, "Utilizing such an exercise could assist in conditioning both select pelvic and scapular stabilizing musculature prior to performing dynamic shoulder movements." As we like to say...PREHAB
Citation: "Electromyographic Analysis of Traditional and Kinetic Chain Exercises for Dynamic Shoulder Movements"