In fairness to Joe Hart, he was not the only goalkeeper at Stamford Bridge who will wince when he sees the replays. Petr Cech got his angles badly wrong for Sergio Aguero's goal. Cech seemed to be anticipating a shot to the opposite side and his body weight was leaning the wrong way. Watch closely and you can see his left leg buckle slightly as Aguero let fly.

There is, however, a good reason why all the scrutiny has been on Hart since Manchester City’s defeat at Chelsea and it is not solely because his mistake, coming in the last seconds, was the decisive one. It is the deja vu that accompanies it, the sense of it being another one to heap on to the list, and the wonderment that there always is in sport when someone who once excelled has started to unravel publicly.

If we are going to be generous, it was the sixth time this season Hart has been at fault when the opposition have scored. Others would contest the numbers are even worse and that there was a degree of responsibility for Romelu Lukaku's goal for Everton and maybe one or two others. But let's cut him some slack and call it half a dozen, starting off with the one he let through his gloves when James Morrison took aim for Scotland against England.

Long list
Fraizer Campbell's first in the 3-2 defeat at Cardiff is another one. There was Andreas Weimann's winner for Aston Villa. Plus, of course, two more against Bayern Munich. Not even three months have gone and, however it is dressed up, it is a wretchedly long list.

Then go back to last season and the first part of Hart's annus horribilis and it is not too difficult to bring the number into double figures. His worst performance of the lot, vulnerable from first minute to the last, was probably England's 4-2 defeat against Sweden last November. By then, Hart had already misjudged a corner, just as he did against Cardiff, for Kamil Glik to head in a soft equaliser in England's 1-1 draw in Poland. At other times, goals have originated from simple handling errors: Adam Johnson at Sunderland; Andy Carroll against West Ham and Steven Davis (from a Rickie Lambert shot) at Southampton. Others, too; in total, 15 or so goals in the last season and a bit can be aligned, to varying degrees, to Hart's goalkeeping.

Totting them up is the easy thing. Understanding what has gone wrong, and why it has reached this stage, from the odd aberration here and there to a full-blown slump, is far more difficult.

Decision-making
At times it has been his decision-making, when to leave his penalty area or when to stay, encapsulated in that moment at Stamford Bridge when Sky's Gary Neville summed it up with three words: "Sunday league football."

In other moments, Hart has lost control of the penalty area from routine set pieces. He has been beaten inside his near post – the goalkeeper’s pet hate – more times than he will care to remember. A couple of seasons ago, he had a slight habit of beating out shots into areas of the penalty box where the opponents could latch on to the rebound, rather than turning them away to the side.

Otherwise, he was pretty much flawless back then, fully deserving his recognition as one of the finest goalkeepers in Europe. Now, to analyse his performance fairly, it is futile trying to skirt over what is so blindingly obvious. Hart has interspersed some good, occasionally excellent, performances with being a threat to his own team-mates and, when it comes to identifying what has gone wrong, there is really no simple answer. A bit of everything, probably.

The souring of Hart’s relationship with Mancini cannot have helped either. Did Mancini want to get rid of Hart at the end of the season? It was not only his form that aggrieved the manager, but his manner behind the scenes, to the point where he looked at him with almost permanent suspicion.

Mancini's judgment was not always clear in his final year, it has to be said, but his impression of Hart does fall in line with the increasingly common view, regularly put forward by Roy Keane, that maybe the goalkeeper has been guilty of blurring the lines when it comes to confidence and cockiness.

Hart is flailing so regularly it could hardly come as a shock if Pellegrini uses the League Cup tie at Newcastle United tomorrow as a chance to examine Costel Pantilimon’s credentials on a more regular basis.

What happens next depends on Pellegrini’s tolerance levels. His manner after the Chelsea defeat, castigating City’s habit of conceding “stupid goals” but refusing to talk about Hart specifically, could be taken either one of two ways. On one hand, it showed that the Chilean would never criticise his own players in the way his predecessor once did. On the other, it seemed as though he had run out of ways to defend his man.

Roy Hodgson will know how it feels, looking ahead to the next two England friendlies and wondering whether it is time to give someone else a go.
Guardian Service