I'm watching some of the videos here:
https://videorulebook.nba.com/rule/back-downs/
It seems to me that whenever a defender legitimately falls down (not a flop), while defending the post an offensive foul is called.
So couldn't a defensive player just stand his ground and let himself get tipped over.
Reason I ask is... I see a lot of post ups where the offensive player "backs in" little by little... why give up room like this? If the defensive player stood his ground and let himself fall, wouldn't he get the call? Are defenders just afraid of falling down? Or would the refs just call this as a flop?