You can spend years, decades, a life-time to tactics, as we see in the Mourinho's, Peps, Pellegrini, Low, among others.

Neville and Carragher debate zonal vs man marking off corners all the time and there is two schools of thought on it. Man marking is very clear and there is always someone to blame. Zonal is one big cohesive measurement and everyone plays a part.

In this situation, IF the defensive structure Poch and his team calls for is zonal, then Bentaleb did his job, should have seen Routledge's movement across the box and picked him up. Equally, Davies' should have seen Siggy peeling and moved over to close that space. The blame, although not entirely his fault, is on Davies' awareness and failure to follow zonal instruction. But, if that cross dropped 15 feet shorter with an unmarked Routledge, they would have scored anyways.

IF the system called for man-marking (which I doubt), then Bentaleb was responsible for picking up Siggy and is more to blame on this. When I look at this, I doubt the system was man-marking as we see Bentaleb check his shoulder for Siggy as he peels, but he keeps on going towards the middle of the box.

What should have happened is Davies' either screams at Vert that Routledge is coming into his space, and dropped off to get to Siggy, or Davies' and Bentaleb should have communicated the switch between Siggy and Routledge. Alternatively, Bentaleb could have hustled himself into the box, and allowed Davies' to drop off. As you can see it's hard to pin the blame on Davies' or Bentaleb completely. I personally would blame Bentaleb a bit more, but he is young and still learning so it's a fact of life that it will happen.

If Siggy wasn't there in this circumstance, perhaps staying at the top of the area incase of a clearance, Davies' would have been correct to follow Routledge. And perhaps that may have been what Davies' thought was happening, if aware of Siggy at all. It was a good goal by Swansea to take advantage of the confusion.