Looking at the Antonelli video on JD, he focuses more on getting/turning "palm up" (AKA what Miggy says and many others) then talking about turning the barrel or knob. Also in the video, you can see that he starts to turn palm up.. but it's more gradual than the short abrupt TTB that TM mentions. He's obviously involving the other major muscles. Looks to me he uses palm up to get the bat on plane early and let the larger muscles take over.... not to generate power/ or early bat speed.. JMHO. Again I believe the hands are an active player allowing the bat to get on plane early ... which allows the major muscles create bat speed deep in the zone
The palm up term is the top hand becoming radial deviated or cocked the same way you might swing a hammer or an axe. That’s the running start so one can stride out get the foot down and not commit yet.
If one ‘turns’ the barrel behind them. Can they still RD or is supination required? If we are trying to get speed behind us?
You can’t stay palm up like JD if your getting the barrel going early behind you. FACT.