How long does he have to be in the new position?

What would make it "long enough"? Remember no time/distance required when defending a player with the ball. Did he establish his position before the ball handler left the floor? Looks to me 100% yes.

I cannot see the video at work. But hilighted above is not proper. Finishing the dribble and being there long enough have nothing to do with the call.

Did B1 establish LGP? Did B1 get to the spot of the collision first? Did A1 go airborne? Did B1 move after A1 went airborne?

Those are things you should be looking at.

Can you please explain why picking up the dribble is relevant?

true, but
 

True,however, if the defender is leaning back and I don't believe the contact was enough to displace the defender had they not be leaning, then I've got a no call. This is what makes it a flop in my opinion. The players lean for a reason. The primary one being to get a PC called against the offense.

But leaning is allowed, and they're still entitled to the spot, so if he's leaning backwards and still gets displaced, it's still a foul.

Now, if he'd have fallen anyway due to his leaning, then there's likely no foul; whether it was a flop or just a poorly executed move to absorb the contact.

They also lean b/c some of them are scared of contact, but that doesn't mean they can't take a pc foul. The judgement as you said is whether or not the contact was enough to displace, but the lean on its own does not rule out the pc, that's all I am saying.

He really wasn't leaning *that* much.

My opinion:

It's a PC foul. The defender established LGP well before the shooter was airborne. Mitigating contact with a small lean is different than flopping. He didn't start to the floor before he was hit.

2-person, I'd want that as the lead. I'm refereeing the defense in my primary. Wish the video played for a few more seconds to see the officials handle the double whistle.

I've got PC. The defender is "at the spot" well before the shooter leaves the floor, and without the benefit of slow motion (which we don't get at all anyways), I can't hardly see any flopping going on.

My definition of a flopping is falling backwards in the absence of contact or far out of proportion with the force of contact. That move is T-worthy in many instances.

Incidental contact that happens to knock over a leaning, off-balance defender is still not a foul: nothing in the definition of foul mentions whether the defender ends up on the floor.

IMO, leaning back and making oneself off-balance actually widens the scope for incidental contact, since it becomes more difficult to put such a defender at a disadvantage.

The OP seems to me clearly a PC foul and not incidental contact.

Even though the player was leaning, LGP appears to have been established, contact appears to be torso to torso. Charge is apparent from this video.

Curious what the T had and why

I understand and agree
 

I agree by rule they are allowed to lean. However, if they lean and the contact is marginal, it's a flop and a no call. You have to ask yourself, what caused the displacement more? The lean or the contact. In the above video, I don't believe the contact was marginal. It was PC all the way. The defender would have been displaced even if he wasn't leaning.

A player falling over does not mean there is a lot of contact. I looked at the video again and the player's feet are in the same spot when they started. If he got "run over" he would not be in the same place. It looks to me that he leaned back and mostly missed the possibility for contact that it would take to get a foul (from me). But if there is going to be a call, it is only a PC foul. But I believe in this case a no-call is the better call if I had to choose.

Peace

We're mostly in alignment, but I'm saying whether the lean contributed to the fall isn't relevant. To me, if the lean would have caused him to fall without contact, then the contact is incidental. If the contact contributed to the fall, however, then it's a foul even if the contact might not have caused him to fall if he wasn't leaning. Leaning is legal, so he shouldn't be punished (by allowing another player to knock him down) for doing it.

Yes
 

But contact is legal too. This is a contact sport. The only contact we penalize is the contact that causes displacement or provides an advantage or disadvantage. If the player is leaning and the contact is marginal, even though it may have contributed to it, I've got a no call. Otherwise, if the offensive player barely touches the chest of the defender while the player is falling back, I would have to call PC. I'm not going to do that. I doubt you will either. Also, I don't believe the rule book really uses the term lean, but it does say that the player can move and brace for the impact. There are better ways to brace for an impact than to lean. However, leaning is moving so it is allowed. But they lean to draw the foul. That is why we can call ( I haven't done it yet) a T for flopping. It's a HTBT and a judgment call. I don't believe either one of our positions is wrong nor are we that far apart on this. My thing is by leaning the defender is already placing themselves in a disadvantageous position. They are putting themselves in a position to be displaced by the slightest of contact to draw a foul. It has to be more than marginal for me to call a PC. It's one of those things that you know it when you see it or at least we should, if we are refereing the defense.