I assume the question came from 'a mover'. If not, if it came from a member, I apologize for being so harsh.
But the idiocy of the case 'the movers' make for 'the move' is beyond belief and needs to be addressed. To suggest THE REAR FOOT OR LEG IS THE ENGINE, the doer, that turns or attempts to turn, at the ground, by creating an external rotation movement of the foot/leg, such that the rear foot turns clockwise for a righthanded batter, is the only way for ground reacton forces to be generated, is 100% POPPEYCOCK. ABSURD. NONSENSE.
Yet that is what they hang their hat on to prove the existance of the move. They keep saying that ground reaction forces are important. (Duh) Given. But then thew spew and attempt to convince the mindless that the only way to create external rotation ground reaction forces is by using the muscles that externally rotate the rear leg. THAT IS TOTAL POPPEYCOCK. One 'mover' claims a physical therapist close to him agrees. OH MY. It had to be a cracker jack box. OR....'the mover' spewed to the physical therapist....misled him/her....causing the physical therapist to make that error.
The 'movers' argument was thoroughly destroyed about 2 years ago, but their hitting religion and gigantic egos will not let the truth penetrate. Demo after demo has been shown to them, proving that the leg CAN externally rotate to cause that external rotation action, and the resulting ground reaction forces, at the foot....or....the leg can DO NOTHING and the same action can be made to happen....or....the leg can even INTERNALLY ROTATE in the hip socket, while SOMETHING ELSE happens, that causes that external rotation of the foot.
But, they would rather deny truth, and continue to sell snake oil, taking your son or daughter down the river with them, than admit they are wrong.
I was wrong once. Maybe twice.

More proof that not only are the movers totally ignorant about how ground reaction forces are created in the high level swing....but that you can not swing in the high level pattern WHILE performing the move....will be presented here shortly.
It is so basic. So simple. It is fraudulent to continue to support the move.
They go as far as to say Albert's leg is externally rotating in this clip....

OH MY.
In his stance, while stationery, BEFORE HE EVER MOVES, Pujols' rear leg is clearly INTERNALLY ROTATED and his hip is coiled causing a FUSION of the rear hip and leg. They are fused into a unit. A unit that will perform AS A UNIT....throughout the swing. The hip WILL NEVER ROTATE.
In his stance, while stationery, BEFORE HE EVER MOVES, there is strong external rotation forces at the ground that would turn his foot clockwise if weight was released. AS his rear leg is internally rotated, the COILING action is going on even when there is no movement seen. The muscles that coil the hip are working AGAINST the muscles that internally rotating leg. The coiling action is strong enough, that if possible, it would snap off the ball of his femur. There is a stalemate in the hip socket. The hip is coiling, The leg is resisting that coil by trying to internally rotate. A stalemate of two strong opposing forces that results in no movement at this point in the swing.
THAT creates the external rotation forces at the foot.
Their belief that external rotation ground forces at the foot must be cause by external rotation of the foot/leg has just been proven to be POPPEYCOCK.
The death of their first belief. A moment of silence please.
Later today.....the death of the move.
Once and for all time.....let's kill it.
Get in your stance.
FIRST....apply external rotation pressure by your foot/leg into the ground. Use the muscles that externally rotate the leg and foot.
SECOND....keep that external rotation of your leg/foot and coil your hips. At this time BOTH the muscles that externally rotate the leg AND the muscles that coil the hips are pulling rearward....BOTH pulling the same direction.
THIRD....feel what is happening in the hip socket. When you externally rotate the leg so as to create an external rotation of the foot, pressure builds in the hip socket such that when you pick up the lead foot, the leg turns/pushes the hip open.
So far so good.
Well....maybe not.
When that hip turns open....is your leg pulling it open....or pushing it open?
OH
MY
It is pushing it open.
The hip (the resistance) is in front of the leg (the driver).
OH
MY
They are really in trouble now.
Call life support.
Good luck whipping your bat with a pushing rear leg. If you turn the barrel with the hands....while externally rotating your leg....you can get some barrel speed out of those hands. OUT FRONT. The hands get pushed out front IMMEDIATELY by that externally rotating leg as soon as you pick up the lead foot. And any barrel turn, during rear leg external rotation MUST be in front of the leg....which means....IN FRONT OF THE CORNER. Double whammy. Pushing leg. Barrel turn in front of the corner.
THAT, folks, eliminates whip. Period.
Some call the hand turn a whip. But it is not. It is a segment that helps create the whip when it works AGAINST the INTERNALLY ROTATING rear leg. But when you rear leg is pushing....it can't work against it. The unloading, externally rotating rear leg pushes the hands in front of it. You can't pull something that is in front of the driver. Without the rear leg PULLING....there is no whip.
Now, since you can't whip, guess what the hips have to do to generate any speed? Because the leg PUSHES the hip open, the movement is quite weak (compared to when you do it right....I'll explain that in the next comment). It happens quickly but it is weak. It is weak in that the barrel feels NOTHING as a result of that movement. So what do you have to do to help out? YOU HAVE TO ROTATE THE HIPS. And that is the KISS OF DEATH....if the high level pattern is your goal.
CHECK.
We learned above that ground reaction forces exist in everything we do.
They exist in bad swings as well as in good swings.
We learned that externally rotating the leg will create ground forces but not a quality swing. It PROHIBITS one very essential element of the high level swing...and that is the whip. It PROHIBITS WHIP by never allowing the resistance to get BEHIND THE REAR LEG.
So....how do we create ground forces AND get the resistance behind the rear leg?
Quite simple.
First....you internally rotate your leg in the hip socket.
Second....you coil the hip rearward. By so doing you FUSE the rear leg to the hip. You create a UNIT. A hip/leg unit. A characteristic of this unit is the hip is coiled BACK AND AROUND the ball of the femur so it's weight is BEHIND the leg. You've already moved resistance BEHIND THE LEG.
As the hip coiled and as the rear leg internally rotated....in summary....AS YOU FUSED THE HIP AND LEG INTO A UNIT....the COILING ACTION causes the external rotation pressure at the foot. THIS IS HUGE. This is way different than the externally rotating leg causing the external rotation at the foot. The difference between....the leg externally rotating to cause the external rotation pressure at the foot.....and....the COILING of the hip/leg assembly causing the external rotation pressure at the foot....is....THE LOCATION OF THE RESISTANCE. When you externally rotate the leg then coil the hip, the resistance will never get behind the leg. The external rotaion of the leg assures that the leg will be the furthest back. The hip coils INTO the externally rotating leg which is further back than the hip. Duh. From that point on, the leg will push. It has to. There is no other option. But, when you internally rotate the leg then coil the hip rearward, the resistance offered by the coiling hip is BEHIND THE LEG. Back and around the leg.
The difference in these two scenarios is very easily felt. Do both. Compare the feeling. As you do both turn the barrel with your hands. Feel the push of the one versus the pull of the other.
More shortly.
CHCHECK