blocking in the back

Watching the last cowboys play, can anyone explain to me why blocking in the back is legal in the offensive backfield ? I have wondered about this for years.

 

Not sure of the play but there are exceptions to blocking rules in the tackle box and 3 yards from the line.

SECTION 7 - CLOSE-LINE PLAY
Close-Line Play is contact that occurs in an area extending between the outside edges of the normal tackle positions and three yards on either side of the line of scrimmage.

ARTICLE 3. ILLEGAL BLOCK BY OFFENSIVE PLAYER
It is a foul if an offensive blocker:

1. Thrusts his hands forward above the frame of an opponent to forcibly contact him on the head, neck, or face; or
   Note: Contact in close-line play is not a foul, unless it is direct and forcible, or prolonged.

Penalty: For illegal use of hands by the offense: Loss of 10 yards.

1. Blocks an opponent (from behind) in the back above the opponent’s waist, or uses his hands or arms to push an opponent from behind in a manner that affects his movement, except in close-line play.

https://operations.nfl.com/the-rules/2021-nfl-rulebook/#article-3.-illegal-block-by-offensive-player

 

So is the close line play thing because otherwise d-line could just spin around them without getting touched?

 

So all those “blocks” of the edge rusher (Harrison, Watt) in the backfield—one arm clotheslining and the other hand between the numbers on his back—ARE legal. Huh.