Well now I know someone who definitely IS NOT familiar with the rules: When is it NOT a violation of rules for a defender to undercut a bigger post player, to shove their hips and legs under the hips and into the legs of the taller post player established in their post position. The UCLA player even put her own body to the side, so she could use her leg strength better in trying to up-root Boston up and out of her post position.
When you are in post position, and a defender undercuts you from behind and tries to take your legs out from under you, what naturally happens? Your upper body falls backwards, causing your balance to fall backwards, and often then causes your arms to flail outward to regain your balance. But was the UCLA player called for the foul for undercutting Boston?
This was a common trick by the NBA's Dennis Rodman, to stick his legs under the rump and into the legs of a taller post player from behind, and in effect try to use his strength to lift UP and OUT to relocate said post player from his established position. It is against the rules and Rodman was often called for it - and many other times he wasn't.
Also defenders from the rear of a post player, when that post player is on offense, will often stick their arms and hands in front of that player to interfere with the passing lane of any pass into the post player. But those post players have the right to clear those areas - either by moving the defender's arms/hands out of the way, or by moving their own arms in front of the defender's arms. In the course of doing this, a post player will already be flailing her arms around from time to time.
And you're also supposed to give an offensive player their vertical space to make offensive moves to the basket when they have the ball. The shorter UCLA player who's head is about shoulder height to Boston, snug up into Boston so close that she could've kissed Boston on the cheek, when Boston was turning (making a post move) to the basket, and her elbow hit the girl in the face. Boston was called for the offensive foul - the UCLA girl seemed to have established her own defensive position - but so many people have tried to claim that Boston was throwing elbows, but all she did was turn with the ball in the air to make her post move.
But that happens all the time in the NBA to shorter players who try to defend post players, or try to block them out for rebounds: you place your face in the area of those guy's elbows, then expect to get elbowed in the face. Players like Cartwright, Rollins, Olajuwon, O'Neil always had strong post moves with elbows out - NOT swinging elbows, but gripping the ball tightly with both hands above their heads, and clamping down those hands hard with their arms, thus causing their elbows to stick up and outward. It's up to Boston to "feel" the defender on her body, and make post moves that separate her from the defender, so that any contact after that will be called on that defender.