i think we need to make a distinction between work rate, pressing and ability to win the ball back
there is no problem with he work rate of any of the players mentioned.......its just done in different fashions
For instance - Kun doesn't press as much but his work rate in the channels off the ball and his attempts to win the ball back when he loses possession are excellent. He physically puts a shift in getting kicked and battered every game....what he doesn't do is sprint at the opposition players when they have the ball and "press them." This maybe cause in his own head he feels he isn't a very good tackler when faced up with an opponent with the ball....his style of movement doesn't lend itself to this though his low centre of gravity and his strength through this does......
Compared to sterling who has similar attributes in that he has strength through low centre of gravity but maybe not so much physical muscle as Kun...however sterlings approach to a player when front on is much more balanced...whether due to confidence or his better balance in this movement i don't know but you can clearly see it. As far as chasing back after thee ball they are both pretty similar its just sterling probably does more of it due to his position on the pitch.
Silva is completely different to both of them - Ive mentioned this over the last few years. Silva's intelligence and reading of the game plus his very nimble footwork and connected to this his ability to manipulate the ball with even the smallest of touches enable him to nick the ball off opponents...he comes in from the blind side quite often and surprises opponents and "nicks it"...he does tackle at times but this he isn't great at and can often give away fouls (More usually however in areas that are not to important/threatening - i.e. higher up the pitch)...if you want to see what i mean about silva touch on the ball, look at how he got the first penalty against jagkelka vs everton.....he was against two defenders and they had actually won the ball for a brief second but silva with his deftness of touch (and possibly a little luck) won it back causing jagelka to trip him)
KDB spends a lot of energy roaming an running across the pitch putting pressure on the defenders of the opposition from the front...he also does a bit of what silva does in "nicking it and reacting very quickly to miss hit passes/getting interceptions and nicking to the toes off of opposition players.
Ferna and Ilky are both combative midfielders and are can win the ball back in all those ways ...they are more balanced and better equipped to do so than the likes of Sergio and the other players
Its all down to physical attributes which is one of the the things Pep keeps hinting at along with mental attributes .....I don't think Pep has any problem with the mentality of any of the players...he keeps saying how happy he is with there approach, openess to do what he wants etc....but he does keep mentioning the abilities of players and type of player.
Nice post simon23. And there's much in this that I agree with.
Yet, there's another angle you didn't mention - sheer physical ability.
Some people can run forever - a football match is a trivial excursion.
Others aren't nearly so gifted. Running for a full 90 minutes is extremely hard or impossible.
In the can't run for 90 category - there's Yaya, Ozil, Silva, etc.
In the running for 90 is very difficult - is KDB.
In the never seems to tire category - is Fernandinho, Sterling, Navas, Nolito, Teves, etc.
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In Pep's system, once the ball turns over, there needs to be an immediate press of the opponent who has the ball by whomever is nearest him.
At the exact same time, everyone else near the ball needs to quickly move to cut off passing angles.
To implement this system for a full 90 requires a lot of stamina - Yaya, IMO, is incapable of this. So too, I think, is Silva, though Silva is going to do his best.
KDB for me, can't last the full 90 either.
But Kun, IMO, has the motor to press for the full 90 - that he does not, is, IMO - perhaps arguably - why he didn't start against Barca.
Nolito, Sterling and Navas can press all day long.
In Pep's system, it doesn't matter if you're great winning the ball back one-on-one - what matters is that you press/shadow-press. Even if you hardly ever win the ball back one-on-one, so long as you press your man if he has the ball, you're going to put the attacker under great pressure; which is all that the system demands.
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If you watch City's games closely...
Our press is great at the start of the game.
And is pretty good until half time.
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Half time and a rested squad appears - pressing is still pretty good.
But, after, say 60 minutes. huge problems arise with our strategy.
No longer is Silva or KDB quickly pressing. As a result, the opponents are able to play it out from the back.
This is why I've downrated KDB defensuveky- he simply lacks the stamina to play Pep's system for the full 90 against a competitive squad IMO.