going to put my two cents worth in here, by giving my take on Leicester's opening goal. Just to demonstrate my view that it's not the 3 at the back system, but the error strewn displays of the players within it. I will be using some very rudimentary images and scribbles to illustrate.
I would say there are 5 phases to the first goal, within each are what I believe to be errors from City players that led to the goal being conceded.
Stage 1: The Kolarov Clearance
Stage 1 shows the backline spread with the purple line. Kolarov has the ball in his own area, you can see the vast spread of City players in front of him, there is a huge gap between the lines which Pep seeks to avoid. This is one of the reasons he likes his teams to play out from the back. Now Kolarov should have 3 options, play long, play inside to Fernando or outside to De Bruyne. Fernando hasn't tracked over enough to provide that option which may have influenced Kolarov, but he still had a very playable ball to De Bruyne which would have retained possession. Kolarov's decision to hoof it long up the centre of the pitch is the critical mistake, and the catalyst for the goal.
Stage 2: Kolarov fails to track Mahrez
Apologies for all of the squiggles but I don't have sophisticated tools. Huth inevitably won the header, the blue curves show that the City players have been turned back towards their own goal after pushing out after Kolarov's clearance. The yellow lines show the huge gaps between the City lines, because of Kolarov's rushed clearance, players like Fernando, Zabaleta & De Bruyne have been caught in no-man's land as Huth's header sails back over them. Crucially, in Phase one you can see how close Mahrez was to closing Kolarov down. By Phase two Kolarov has let Mahrez go completely and both he and Slimani are completely unmarked. This then allows Mahrez to play a ball unchallenged to Slimani to set up Stage 3.
Stage 3: Whose line is it anyway?
This image (badly) shows the positioning of the back 3, and how they are not holding one line. In fact, they've got themselves into such a disorganised pickle they have their own clearly definable defensive lines. This creates a big problem as illustrated below.
Now this is where it comes to my opinion, but whilst there are attacking benefits to a high defensive line, the key part of that phrase is "defensive line" i.e. one of them. The onus here for me falls on Stones, he is the central player in that 3 and he is also the deepest. There needs to be clear leadership from one of the three (like Vinnie at his best) and clear instruction on how to deal with this situation.
Now for me this falls into one of two errors by Stones. The first, and gravest if true, is that Stones fails to read the situation properly. Slimani has taken his touch, and this pass is the most telegraphed pass you will see all season. Stones's rough field of vision (or at least his sphere of what he should be aware of and alert to) is in blue. Stones should read that:
-Vardy is committed to making a run off his left shoulder.
-Vardy is the only viable passing option for Slimani.
-Slimani's lack of technique means it is evident even from the still that he is telegraphing this pass.
-He is the last line of defence.
Now if Stones didn't read the situation, then we have a problem because he'll endlessly make these errors of judgement. The second option is that he made the wrong call to deal with it. At this point, and yes hindsight is a wonderful thing, with Stones backpedaling and Vardy already on his run, for me Stones has to realise he cannot win that foot race in those circumstances. Therefore for me, as outlined with the purple arrows, he should step up and instruct Kolarov to do the same. By stepping up he has the chance to play the committed Vardy offside, or alternatively pressure Slimani into misplacing the pass. At worst, Vardy somehow beats the trap and ends up in the same situation anyway, a goal-scoring opportunity with Bravo. For me the sensible option for Stones was to step out, and not backpedal.
Stage 4: Still time to rescue this.
Stones backpedals, and Kolarov commits to chasing Vardy. Vardy is now off and this pass is about to be played. This is milliseconds after the previous image but Stones has already back-pedaled several steps and AK is committed to the run. At this point a signal from Stones and one last change of decision, and stepping up, can play Vardy clearly offside. It leaves it in the hands of the linesman, but at this point Vardy is ahead of AK and turned onto his run whilst Stones is still facing the ball. At this point neither Stones or Kolarov can get the ball off Vardy. For me this is the final chance for Stones to step up and make the right move. He fails to do this twice.
Phase 5: Bravo fails to read the play
We move the footage on, Vardy has run clean through. Now there is a risk of him being lobbed, but if Bravo stands up then I think he makes the chance much harder for Vardy. The fact is though, Vardy has run clean through and now has the ball, and Bravo is only just coming off his line. For me, Bravo reacts FAR too late to the move, and should be anticipating this chance once Stones starts to backpedal and Vardy is on the turn. He should be out much quicker and at the edge of the blue box area (6 yard line side), thus making him bigger in the goal and starting to narrow Vardy's angle. Instead, the ball is almost past Bravo before he reacts to try and save because he is still on the move trying to narrow the angle, and because he hasn't come out far enough he's left the angle open to the far post, the one area a right footed player will naturally aim for. If Bravo had reacted quicker, and narrowed Vardy's angle, he takes away the far corner and has much more chance (although Wickham's goal suggests otherwise) of preventing Vardy scoring either in the middle of the goal or to his near post, which is the much harder shot for a right footer.
So a very long post, with big images with amateurish scribbles on, but I hope my points get across. In summary it comes down to five key phases:
1. Kolarov goes against Pep's teaching and clears the ball long with his team out of balance, and with a viable passing option to De Bruyne available.
2. Kolarov fails to track Mahrez properly and put him under enough pressure to prevent him playing an uncontested pass.
3. The back 3 take up their own defensive lines instead of one uniform line and Stones decides to backpedal instead of step up and play Vardy offside.
4. Given a second chance to step up, Stones fails to do so and Vardy will now have an uncontested chance at scoring past Bravo.
5. Bravo reacts far too slowly to the unfolding action and fails to close down Vardy quickly enough, resulting in Vardy getting a clean strike into his preferred area of the goal which was unguarded.
and for me, none of it is down to playing 3 at the back. Feel free to completely disagree, I'm not Pep after all.