Arsenal and Liverpool are out of the title race because of bad defending
Inspecting the league table tells you everything about why Liverpool and Arsenal have failed to launch a title challenge this season. The points column shows Arsenal 13 points behind Chelsea (with a game in hand) and Liverpool a further point back, but the "goals for" and "goals against" column illustrates precisely why.
League leaders Chelsea have scored 55 goals, the same number as Liverpool. Arsenal, meanwhile, have scored 54 goals, and considering they've played one fewer game than the others, this means they're effectively scoring at the highest rate in the division. Going forward, both sides don't have many problems. The "goals against" column, however, shows Chelsea have conceded only 19 goals, whereas Arsenal have shipped 28 and Liverpool a hugely concerning 33.
Alternatively, Chelsea have kept 13 clean sheets, Arsenal just eight, Liverpool only seven. It might not be a particularly major revelation, but the reason these two sides are struggling to challenge for the league title this season is simple: their defensive record isn't good enough.
For Liverpool, this has become a familiar problem. During the Rafael Benitez era, Liverpool usually boasted having among the best defences in the Premier League: their goals against figures of 25, 27, 28 and 27 between 2005 and 2009 looks quite extraordinary in hindsight, considering that they've conceded 50, 48 and 50 goals in the past three seasons. Their current rate means they're set to concede a similar number of goals once again.
It's usually the back four that gets blamed for conceding lots of goals -- goalkeepers Simon Mignolet and Loris Karius haven't exactly escaped blame either -- but perhaps the greatest problem for Liverpool is that they're not protecting the back four effectively enough. That, more than anything else, was Liverpool's strength during Benitez's reign: he sacrificed attacking spontaneity for defensive structure, using wide players who protected the full-backs more effectively than they created chances and constantly shouting '"Compact!" at his team, ordering them to defend with 10 men.
Under Jurgen Klopp, Liverpool's approach has changed dramatically. They are defined by their approach without possession, but Klopp's love of counter-pressing is primarily an attacking tactic: it's used to win possession while the opposition are starting their attacking transition and leaving spaces at the back. It's unquestionably a useful tactic and has proved particularly effective against major opposition, particularly sides like Arsenal that like to build from the back. But once the press is bypassed, Liverpool's defence can be too easily exposed.
Jordan Henderson has been among Liverpool's most impressive performers this season in the holding role, but it's no longer enough to protect the defence with one man. It's a collective effort, and while Liverpool's work rate itself is not up for question, their default movement of pressing the ball means the defence sometimes has a huge amount of space to cover.
Some teams can get away with that, but Liverpool's defence itself isn't particularly solid, as Klopp has constantly changed centre-back partnerships. At times he's been unfortunate because of injuries or slightly peculiar reasons for absences (Mamadou Sakho and Joel Matip), but there's still no clear first-choice centre-back partnership on the same wavelength. Matip and Ragnar Klavan have both looked excellent in some matches before making needless errors the following weekend: centre-back play is all about consistency, something Liverpool simply don't have.
Full-back remains something of a problem position, too. Liverpool don't have a proper left-back: Alberto Moreno's complete lack of defensive awareness means James Milner has deputised in that position, and while he performed competently in the first half of the season, he's recently looked tired and poor in a positional sense. On the opposite flank, Nathaniel Clyne has been somewhat underwhelming this season and now looks less secure than in his Southampton days.
The one caveat is that Klopp has been forced to cope with a huge number of fixtures during his time at Liverpool so far, with runs to both the Europa League final and League Cup final last season and a run to the League Cup semifinals this year. Klopp hasn't had a particularly long run on the training ground with his players, and defensive organisation usually stems from working on shape week in, week out. Now, however, Liverpool have only one midweek fixture for the rest of the season. Klopp has plenty of time together on the training ground with his players, and a major defensive improvement should follow.
Arsenal's defensive woes are slightly more surprisingly. In three of the past four seasons they've conceded fewer than a goal-a-game, so their current concession rate is somewhat unusual.
Again, this has largely been about the lack of protection from the defence. While Shkodran Mustafi was guilty of a wretched error against Bayern Munich, he's largely been solid since his arrival and has formed a decent partnership with Laurent Koscielny. Hector Bellerin has been troubled by injury but is a fine defender as well as a crucial attacking weapon, while Nacho Monreal remains the typical, unfussy full-back who is 7/10 every week.
The disappointing thing about Arsenal, though, is that they haven't solved their midfield issue.
Granit Xhaka was set to be the perfect holding midfielder, a tough-tackler also capable of distributing the ball well over long distances. Arsene Wenger seems particularly keen to protect his defence in big matches: after a few years of often fielding one defensive midfielder alongside more of a creator, he's often used two of Xhaka, Francis Coquelin and Mohamed Elneny. But none have enjoyed particularly good seasons, and there's no obvious partnership between any of them -- or between them and another of Arsenal's more attack-minded midfielders. Some individual mistakes have been infuriating: the way Coquelin allowed Arjen Robben inside to open the scoring in the 5-1 thrashing at Bayern was particularly notable.
Two poor defences means this weekend's game will surely produce goals: the past two meetings between the sides have produced no fewer than 13. It's also the main reason, however, why these sides are forced to fight for the Champions League places rather than the title.
Michael Cox is the editor of zonalmarking.net and a contributor to ESPN FC. Follow him on Twitter @Zonal_Marking.