Controversy and Replay

At best, officiating is difficult. 

During set three, Winchester leading 28-27 a controversial play occurred. The lead official called a violation (under the net) and after consulting with the floor official, the play was ruled a replay and no point was awarded.  

Real-time, I saw the player go under the net (bottom of the screen) into Melrose territory. I don't know the nature of the discussion and ultimately it didn't change the outcome. 

The original feed (beginning at 1:27:24) allows you to view in slow motion. 

Penetration Under the Net

The short answer to whether you can go under the net in indoor volleyball is yes, but there are considerations. For example, you may penetrate into your opponent's space provided you don't interfere with play. This means you can't make contact with an opponent or get in the way of an opponent who is getting into position to make a play on the ball or getting set to play defense.

Hands and Feet Only

The International Federation of Volleyball allows a player to reach under the net into the opponent's area with the hands and feet only. Any other body parts are prohibited. In addition, some part the penetrating hand or foot must be in contact with the center line or be directly above it.