Before I bought my son the Clean Fuego training tool, I noticed that his fingers were slipping to the side of the ball on his 4-seam fastball.
The upside to this was that he was getting cut and glove-side movement, but the downside was that he was sacrificing velo.
As we all know, velo is king in contemporary baseball, and exchanging velo for movement on the 4-seamer was not something we were willing to do.
The Clean Fuego training tool forces one to get behind the fastball with a strong wrist in order to achieve clean spin.
If the ball wobbles, you aren't getting clean spin, and you aren’t getting behind the ball as much as you can. Keep throwing it until you get a clean backspin. This will help you stay behind the baseball.
Keep in mind that the Clean Fuego does not need to be vertical or upright as it travels through the air. The ball can be canted or lean one way or the other. The key is how true the spin is.
Keep throwing the Clean Fuego until you achieve a clean spin. Then switch to a real baseball and try to replicate your technique. This will help you stay behind the fastball.
And staying behind the fastball will result in more velocity.
Stay hungry, friends.