Ryan Armstrong has worked at The Baseball Zone for 8 years. He is the associate head instructor, the head pitching instructor, and the director of high performance programs.
Quarter Turns is a drill we use to promote rotation and weight transfer through the swing. We do this by starting the drill in a "quarter turned" position, thereby already getting the hitter into a position on the way to rotation and transfer.
When doing the drill we just need to start in a regular stance and, as stated, just start the lower half into its rotation and weight transfer or "pinching" of the backside to the front side. From here, the hitter can simulate an at bat, either off a tee or with a partner doing front toss. We find that the Quarter Turn drill can help the hitter more naturally get better rotation and transfer after being artificially placed in a quarter turn start. Obviously the intention is that by working on this it will then help transfer to their regular swing.
Coaching cues would be to watch for the hitter's finish to include full rotation as well as transfer to the front side with little to no weight on the backside while maintaining a balanced hitting position.
Quarter Turns can be done by anyone, but are especially helpful with players who finish with too much weight on their backside, which can limit power as well as the distance that the bat plane stays on plane with the pitch.