It was exactly the same against Villa in the last game of last season.
Stones does a job at right back, but the attacking side of his full back role is slow and unnatural. That in turn makes Mahrez ineffectual and therefore the opposition defence doesn’t have to track as far and so can stay compact, closing the half spaces and stopping our attacks more easily.
If we’d have had Cancelo and Gomez as full backs, we’d probably been about 4 up and not needed a worldie from Stones.
Ah well, late comeback wins are superb though.
