Weighted.Underweight Ball Study

has anyone done a study on the use of weighted and underweighted balls to increase velocity? Anyone come across such a study?

I’ve read fastball fitness by the NPA and one other study on them.

Look for underload and overload principles.

Effects of General, Special, and Specific Resistance Training on Throwing Velocity in Baseball: A Brief Review (DeRenne et al, 2001)
Effects of Baseball Weighted Implement Training: A Brief Review (DeRenne et al, 2009)
Increasing Throwing Velocity (DeRenne, 1985)
Effects of Under-and Over-Weighted Implement Training and Pitching Velocity (1994)

Those studies may help.