Block or Charge?
 

A1 is guarding B1. A1 has established LGP. B1 begins their dribble towards the basket, A1 anticipates, moves latterly and has now beat them to the spot but still moving. B1 continues forward and makes contact.

1) If A1 goes down from the contact (even though they weren't standing completely still) is it a charge?

2) If B1 goes down or loses the ball, no foul?

#1...Sound like a PC foul to me....as long as A1 (the defender) was not moving towards the opponent at the time of contact.
#2...possibly a no call...if the potential foulee is the one on the floor or has lost the ball, have they gained any advantage trough the contact or put their opponent at any sort of disadvantage.

Also, note that, traditionally, A is used for the offensive team and B is the team defending.

Well you said the defender was moving forward and makes contact. If that is the case then in #1 you would not be standing still.

I have a foul in both situations because the contact clearly caused an advantage or disadvantage to the players. And anytime contact causes someone to lose the ball and the player was not in a legal position, then that is a foul. But the problem I have with the question is the first play the defender is either moving forward or he is not.

Peace

The rule does not require that the defender be stationary upon contact. The defender is even allowed to have both feet off the floor upon contact. The defender just can't be moving forward and initiate the contact.

I think you misread the OP. He is using "A" for the defense and "B" for the Offense.

You are right he is switching the classifications.

Peace

Yep. My bad on the initial use of A and B. In my scenario A was the defender, B was offense. Thanks for the correction.

Just understand A is used as offense and B is used as defense in the Rulebook and Casebook. I focused on the last sentence before the numbers.

Peace