I copied this from another site but this guy sums it up better than I ever could. Kamala Harris would be proud of this word salad!! Typical NCAA. Here you go:
Let's start with the definitions of a block and a charge, shall we?
Rule 4, Section 9, Article 1 defines a block as follows:
Blocking is illegal personal contact that impedes the progress of an opponent.
Rule 4, Section 12, Article 1 defines a charge as:
Charging is illegal personal contact by pushing or moving into an opponent’s torso.
Now, the question regarding block/charge has to deal with establishing position. Let's look at the definition of the term guarding, since that is part of the key to understanding who gets to establish position.
Rule 4, Section 35 addresses the definition of guarding. Article 1 defines guarding as:
Guarding shall be the act of legally placing the body in the path of an offensive opponent. The guarding position shall be initially established and then maintained inbounds on the playing court.
Seems straightforward enough, but it doesn't really address establishing position. Articles 3-5, however, does:
Article 3 states:
Every player shall be entitled to a spot on the playing court, provided that such player gets there first without illegally contacting an opponent. (Exception: Rule 4-35.7)
So how does one establish position when guarding a player with the ball?
Article 4:
To establish an initial legal guarding position on the player with the ball:
a. The guard shall have both feet touching the playing court. When the guard jumps into position initially, both
feet must return to the playing court after the jump, for the guard to attain a legal guarding position.
b. The guard’s torso shall face the opponent.
c. No time and distance shall be required.
d. When the opponent with the ball is airborne, the guard shall have attained legal guarding position
before the opponent left the playing court.
(Exception: Rule 4-35.7)
So this is what it takes to establish position, and I think that points (c) and (d) are the critical ones that cause the most consternation among fans. Maintaining position, however, takes a bit more effort, right?
Article 6:
To maintain a legal guarding position after the initial position has been attained, the guard:
a. Is not required to continue having the torso face the opponent;
b. Is required to have either one foot or both feet on the playing court (cannot be out of bounds);
c. May raise the hands or may jump within his or her own vertical plane;
d. May shift to maintain guarding position in the path of the dribbler, provided that the guard does not charge
into the dribbler or otherwise cause contact;
e. May move laterally or obliquely to maintain position provided such a move is not toward the opponent when
contact occurs;
f. Is not required to have the feet on the playing court when shifting in the path of the dribbler or when
moving laterally or obliquely; and
g. May turn or duck to absorb shock when contact by the dribbler is imminent. In such a case, the dribbler
shall not be absolved from the responsibility of contact.
That's what the rules say about getting defensive position and how a defender can go about drawing a foul. As long as they meet the conditions set above, I believe that the call can be made. A lot of information has to be recalled, and in only having a split second to assess the situation and make a call, I can see where a lot of the controversy (depending on what is called/not called for your team) can come from.