The Sexton Loop

Many of Ireland's best attacking movements are linked to the Sexton Loop.
Sexton passes down the line, and then runs behind the player catching the ball. Sexton then loops around to take the pass, before drawing and passing again in the new line. 

When the camera angle shows from above the stadium roof, it is clear that blockers are protecting Sexton. 
It is obstructive running, and they did this a few times in the Scotland game.

Sometimes Sexton does this legitimately, but sometimes he gets away with obstructive running and blockers (like American football)

I can't say I've seen a particular issue with obstruction. The entire premise of the game as it is now is to move behind screens. I haven't seen a point where the defence was unable to slide and catch him if they read the movement correctly. I'm not necessarily keen on this kind of move as a pass is quicker than the loop, and cut balls or missed balls can be more impactful. Not much of an issue. When Ireland are most dangerous with the wide game is when their pins in the form of direct runners hold the line, that's when the Irish are most dangerous. Against the Boks they were very good at holding the pass, and letting the rush move past them, then attack the space in behind. Or a ball over the top outside the edge defender. The key thing here is that they are very attune to what is happening, and make very quick decisions. 

Nonsense, it is not American football. 

b)  Running in front of a ball-carrier. A player must not intentionally move or stand in front of a team-mate carrying the ball thereby preventing opponents from tackling the current ball carrier or the opportunity to tackle potential ball carriers when they gain possession. 

……

In the case of Ireland clearly they are not moving or standing in front of the ball carrier. If anything the ball carrier is moving behind them.

There is some interpretation here, but I think as long as the players he runs behind don’t change their angle or run into  the defenders….it’s legal. Although it might be interesting to see what happens if a defender deliberately runs into one of the players in front and makes a fuss.

The double wing, which could also be claimed to be obstruction has been legal for a long time.

Bigger problem is the screen in front making contact with defenders, as in the first try against Scotland where a key defender (Scot 2) was clearly taken out by Ire 4. That ended up creating the gap Ringrose used to break the line.

I assume you mean the second try Pakie. There were two runners pinning two defenders. They were held, and Sexton looped behind them. There was a 2v2 and Sexton put Aki between Scot 12 and 13. This breach was where they broke for the try. Why do the Scots fail here? 13 is ball watching, and 12 is flat footed. It's passive defending. Prior generations were much better at supporting the inside and outside of the challenged defender and adjusting. So many tries are scored because simple assignments are not picked up. A loop is no more difficult to defend than a switch, blocker, or slider play. Lazy and passive defending. 

https://www.centurion-rugby.com/blogs/rugby/obstructing--in-rugby

Obstructing and knocking rules in rugby

Players can only tackle a player in possession of the ball. If a player deliberately obstructs the way of his opponent, because he thinks is rival stands a better chance of getting to the ball first, this is disallowed.

Charging and pushing - you cannot charge or push an opponent when running for the ball unless the contact is shoulder to shoulder.

Blocking - if you deliberately block an opponent to try to stop them from tackling one of your team-mates or you try to shield a team-mate, this is also disallowed.

Standing - if you stand in a position which could stop an opponent from playing the ball this is counted as an obstruction.

Running - players who are running with the ball after it has left a set-piece cannot make contact with a team-mate in front of them.

Flankers - cannot block the opposition's scrum-half whilst they are advancing around the scrum.

All of the obstruction offences outlined above are awarded with a penalty to the opposition. The offender could also find themselves shown a yellow card which could accumulate to 10 minutes in the sin-bin.

The whole point of the loop is to create numerical advantage by having the defender bite on the first receiver. If they choose to tackle that first receiver and he slips a pass to the looping runner too bad. There is nothing stopping the defence from using a drift where the outside defender takes the looping player and the inside player takes the screen runner. Show me an account of this loop where the defence had no chance to stop the play. It's called a screen for a reason: deception. Pinning the defence and allowing the looping runner too artificially add numbers to the line. This isn't rocket science. If you think this is bad, what about more complex switch plays? 

This is one example as Sexton runs onto the ball. The Scotish players was running at pace but is blocked.

The 1st try, before Sexton passes to RingRose

If you change the play speed to slow it is easier to see. 

https://youtu.be/a_ri6Tkgikk?si=Tcz-iA-cOKbnF4Z3&t=27

When you look from behind, and from above it is sometimes easier to see (if it did happen)

On the first try, Sexton may run behind blockers, and then Ring Rose appears to do something similar. If you check  at 31 seconds - a blocker actually knocks a Scotish runner off his feet, with another blocker closing the space by running at an angle. 

Then on the 2nd try, Sexton appears to use blockers again.

Sometimes it is marginal, but during the match, a few tries seemed to break the defence just a bit too easily. 

One thing is clear, Sexton is Ireland's key man. If the All Blacks can close him down or run into his blockers to get penalties

I assume you mean the second try Pakie.

Nope, first try Deus.

I4 runs into S2, completely removing him from the defensive line.

I13 then breaks the line exactly where S 2 would have shifted to had he not been taken out.

Also known as 'the hula-hoop dupe'

This has been my bug bear for ages with Ireland and they keep getting away with it. What makes it hard to blow up is the fact that the create a diamond. What this doesn't show, is the pass out the back. 

So. SA normally has a single big ball carrier that hits that 1st channel with a supporting player latching on. 

Here, they have about 4 forwards and 2 backs, because the first receiver is in front of Sexton, all he does his slip the ball out back to Sexton who now has players in front of him. Technically, it is fine because the other players were onside during the first play and part of the move. The thing here is that they do it so quickly and accurately that it is less than a second in which the transfer the ball. 

What this does is create doubt. Any player in that formation can touch the ball. It is really smart play. 

There forwards don't try to bask the ball but always run on the week shoulder of the defender and always glance the tackler. They hardly ever go head on or try run over the player like SA does. 

So that play to me is brilliant. 

But they do cause obstruction, a lot. The also make contact, a lot of the time, 

The main problem is that the cover defender is taken out. So even though the ball has moved on, the player sweeping often gets taken out. This is an old ploy and used many times back in the day by Australian teams. This is something from Rugby league where they run these screens. 

I think it should be banned. It doesn't put the player in a 1 on 1 situation. To many player in from of the ball. Defender have to run around. 

I would make sure that those players who run the screens make contact with my defenders and I would make a big scene out of it and put the ref under a lot of pressure. 

I would train my captain to quote the exact sub section of the rule like Mozart did to the reff. I would put doubt in reffs head. 

On one hand the ref is told to let the game flow, so marginal calls like this, team will get away. But image if 3 players gets skitteld over. 

This is what I hate about Irish play. It is border line cheating and no team have figured how to expose them for this. 

With out this play, they are not that effective

Also, remember that amazing Am try but then got cancelled because one of our players glance Whitelock. It was a 50/50 call but he made sure the ref knew about it. In the end it worked. 

Compare to what Ireland does in comparison, almost 90% of their tries would have been disallowed. 

It is because they flood that channel and it is really hard to convince reff as the players are allowed to stand their ground