Whether Brendan Rodgers has played a back three or a back four this season, there can be no doubting the fact that, when Daniel Agger is in the side, Liverpool just seem to defend better.

In 13 games this season, Liverpool have conceded just four in six of the games that the Dane has started, and 12 in the seven that he hasn't.

Of those four goals in six, three were given away in last week's frantic Merseyside derby. Otherwise they have given away just one goal in five games with him in the side.

Rodgers used the result against Everton as an excuse to drop him from this week's game away at Hull, and they suffered their worst result of the season as a consequence.

You would have thought the fact that Agger has started in every one of Liverpool's four league clean sheets so far this season spoke for itself. The statistics are very much in his favour.

But apparently not, so how come he hasn't started more often?

Squad rotation could be attributed here, but in Liverpool's five games between their 3-1 victory away at Sunderland on 29 September and their 2-0 loss away at Arsenal on 2 November, Agger started on the bench and Rodgers started with a back three.

For nearly half of Liverpool's games so far in the Premier League, then, he has effectively been their fourth choice central defender. 

But if it is the case of changing it around to keep things fresh, how beneficial even is regular rotation in the heart of defence? There is little surprise that the best defensive units in the league so far this season have belonged to Arsenal and Southampton, who are the only teams in the top half to have had an established centre-back partnership from the off.

Rotation shouldn't really be so much of a necessity either. Liverpool have no European commitments this season and have suffered an early exit from the League Cup. It seems as though Rodgers is chopping and changing more in an attempt to keep everyone happy than anything else.

It's possible that Agger has suffered at the hands of fellow left-footer Mamadou Sakho. It is clear that the Frenchman did not come from Paris Saint Germain in the summer not to play.

The two have started just once together this season, in the 1-0 loss at home to Southampton, and even then Sakho was played at left-back.

The abject loss at Hull on Sunday was the first time neither had started. Needless to mention again that it didn't go great. 

Recent history tells us that managers do not seem to like to play two left-footers in central defence. Roberto Mancini seemingly used to go out of his way last season not to start Matija Nastasic and Joleon Lescott together for Manchester City.  

Liverpool now have two home games in the next few days, against Norwich and West Ham, that are eminently winnable.

The Christmas period, though, looks a lot more tricky and Rodgers could really do with establishing what his best defensive unit is before they face Spurs, Man City and Chelsea in the space of fourteen festive days.

Especially if the Reds are to maintain any hope of still being in sight of the top by the turn of the year.

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Premier League
Daniel Agger