the screenshot should clear it up. You can't call semedo, doku's man simply because he's the rwb and doku's the left winger. Doku is in a perfectly fine position pressuring the ball, nobody is out of position there at that point. Rico simply doesn't switch on quickly enough, he starts jogging and the sprint doesn't come soon enough.
You'll notice their striker has peeled off. It would be comical to see stones stay with the striker there as the ball goes to the opposite side, when the ball is on the other side, the whole unit shifts across and the fullback tucks in on the last man, that's just the basics of a back line, you won't see 2 centre backs split, unless you watch united.
I've seen the video, that's where the screenshot has come from, where pep wants him to play in possession has no influence on this goal. He's already back in the right back position before the ball even enters our half, at that point, he's the conventional fullback and expected to do the basics of a fullback. Gvardiol goes towards the ball, dias shifts across, stones positions off dias and Rico tucks in. They all actually attempt that, the error is Rico doesn't do it quickly enough.
He's another screenshot as the ball leaves semedos foot, you surely cannot be suggesting stones should be with the goalscorer there? Stones has to position himself off dias, he cannot leave a chasm between his centre back partner. It's a clear basic error from Lewis.
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