this.
Basketball Rules | Better Basketball
"Officials should only make a foul call when contact is made. Just like the basketball rules term reaching in, over the back is not a foul until contact is made then it should be called a pushing foul.
Even if a smaller player has good rebounding position against a taller player, a foul should not be called if the taller player can get the rebound without touching the smaller player."
Who initiated the contact also should be considered. Barnes had position, but Williams did not initiate the contact. It was a high rebound, Williams got possession first before any contact was established, and then Barns fell back into him and grabbed his arm. I bet Barnes would acknowledge it wasn't an over-the-back.
Hate him or not, Teddy V's crew made the correct no-call on that play.