Interpretation or clear obstruction?

Firstly let me congratulate the ABs on their win today, they were clearly on top for the whole game and barring any miracles look set to be the World Champs by this time next week ...

However something that's been bugging me for some time is a tactic I've seen them use at numerous breakdowns which to me looks like obstruction, but which rarely seems to attract the interest of the officials, so I'm wondering if I'm misunderstanding the laws.

I understand you can 'clear out' defending players at the ruck but I thought they had to actually be at the ruck to do this. Often when an AB player is tackled, the supporting players seem to go well beyond the breakdown and tackle the defenders coming in a good yard or more in front thus stopping the defenders from competing for the ball. An obvious example of this was one ruck where an AB player tackled the Ozzie hooker around the ankles and held on to him a yard or more on the wrong side of the ruck, stopping him from getting to the ruck, and although he was clearly seen struggling to get his feet free in full view of the officials nothing was done ... Surely this is plain and simple obstruction?

Once again this is not a pop at the ABs win as they fully deserved it but I'm puzzled by what I see and wonder if interpretation is different to what I thought was the law?

First rule of International Rugby. 'Them lads in black get away with bloody murder' All blacks are historically the game's best 'rule benders'