Offside at what?

Sosene Anesi of the Waratahs races downfield. Two Lions players, Burton Francis and Wigan Pekeur, stop him. Drew Mitchell and Dean Mumm support Anesi who drives in before going to ground.
 
 Mitchell stands watchfully over Anesi and the ball comes back quickly to Phil Waugh who passes to his right.
 
 The referee gets advice from his assistant that Lions were offside in midfield. The referee penalises them.
 
Why were they offside? Identifying the phase of play is important.
 
Go back to the position where Anesi and the ball are on the ground with Mitchell crouched over them. There was no contact with a Lions player and thereforer no ruck and therefore no offside line at a ruck.
 
Go back. There was a tackle before the ball came to Waugh. There was a tackle. Anesi was carrying the ball when he was held and brought to ground.
 
But there is no offside line at a tackle. There is a stipulation about how you may get involved in a tackle, but no offside line. That was not a reason.
 
Wind back again.
 
When Anesi made contact with Francis and Pekeur and Mitchell and Mumm joined in, there was a maul.

Law 17 DEFINITION
A maul occurs when a player carrying the ball is held by one or more opponents, and one or more of the ball carrier’s team mates bind on the ball carrier. A maul therefore consists of at least three players, all on their feet; the ball carrier and one player from each team. All the players involved must be caught in or bound to the maul and must be on their feet and moving towards a goal line. Open play has ended.

That maul continued till the ball emerged - the successful end to the maul.

The Lions players in midfield were offside at a maul.