Aidan O'Hara: 'Klopp has found 'creative solution' but set-piece vulnerability still lingers
It's a measure of where Manchester United find themselves in terms of playing style and ability that they go to Anfield tomorrow with the kind of mentality usually reserved for mid-table teams and relegation battlers: keep it tight at the back and hope to nick something from a set-piece.
In the last two seasons, United have managed the first part of that equation quite easily, with Mo Salah's runs inside from the right-flank being regularly thwarted by Ashley Young who, as a right-footed player at left-back, is happy to have a winger cutting inside into what is also his strongest foot.
If Liverpool go for the throat tomorrow, Salah may well play centrally which will create a different set of problems to the ones encountered by United at Anfield in the last two seasons, which, depending on your perspective, have either been bore draws or Mourinho masterclasses.
In three games at home to United since he has taken charge, Klopp hasn't seen his team score a goal.
Going to the league leaders and leaving with a point is rarely a bad result but another dose of one-shot-on-target sterility would only add to the case that, in the same way that the last thing to leave a boxer is the power of his punch, Mourinho will always be able to count on his negativity by shutting an opponent down.
It would be foolish, however, for United to get dragged into a slugfest with Liverpool but, even though Jurgen Klopp's team have the best defensive record in the league, there have been several occasions when they have relied on the expertise of the assistant referee, and it's here that United will likely seek to exploit.
On Sky's Monday Night Football two years ago, Klopp outlined his thought-process on defending set-pieces, which usually consists of one player marking the space in front of the front post, three defenders on the edge of the six-yard box whose job it is to attack the ball and four in front of them who are meant to block or disrupt the run of the attacking team.
From this particular corner (Figure 1), Hull scored after winning the second ball and, because of Liverpool's lack of height at the time, it meant that they had to find other ways of defending against teams who used set-pieces as a weapon.
In developing Joe Gomez and signing Virgil van Dijk and Alisson, Klopp has solved the "physical quality" issue which means that hopeful crosses swung into the box are dealt with in way that they deserve rather than causing the type of panic which comes from having the indecisiveness of Simon Mignolet or Lorius Karius minding the house.
Yet it's the "creative solution" that Liverpool have employed this season which United, and others, will seek to exploit given its reliance on split-second timing and assistant referees being at the top of their game.
When defending set-pieces, Liverpool now like to leave the area in front of their goalkeeper as clear as possible, allowing both Alisson space to claim the ball or, if he is only able to parry it, it means that a striker following up should be left standing in an offside position.
The problem with such a high line, however, is that it can be exploited relatively easily by an opponent running from deep, who in turn can set up several of his team-mates in front of the goal with no defenders goal-side of these players.
At crucial times in four of their 16 league games this season, Liverpool have faced set-pieces and the manner in which their opponents attacked suggests they have spotted a weakness, even if they've been unable to exploit it because of Liverpool's tactics, their own error or a mistake by the linesman.
In the home game against Fulham, the visitors had a corner from the right and Liverpool set up in the same way as they had done against Hull two seasons ago.
However, once Fulham played the corner short, Liverpool's defence pushed straight out without much care or attention to the players they were marking.
As Liverpool sent only one player out to defend the short corner, it was easy for Fulham to create an overload (Figure 2).
When the ball came back to Fulham's Tom Cairney , he was under no pressure and had the time to spot a player and space in which to aim at (Fig 3, shaded).
It's a fairly basic principle of defending that the riskiest time to attempt to leave somebody offside is when an opponent has good possession, yet Liverpool ignored this with three defenders (Figure 3, circled) all on the wrong side of the players they were meant to be marking.
When the cross came in, Aleksandar Mitrovic scored with a free header but was deemed offside, even if Andy Robertson was slow to get out and arguably kept him onside.
From the free-kick, Liverpool broke and Mo Salah scored 14 seconds later to keep the Anfield train rolling.
Against Burnley, they conceded when the eventual goalscorer was certainly offside but, again, it came about because Liverpool had chosen to entirely clear the six-yard box from an inswinging corner (Figure 4), even though it meant players were unmarked.
Once James Tarkowski wins initial header at the back post and heads it towards the shaded area, Burnley's Sam Vokes (circled) is free in front of the six-yard box and should score but is foiled by Alisson.
The eventual goalscorer, Jack Cork, is behind Vokes in an offside position meaning Liverpool had reason to feel aggrieved but it's generous to argue that a solid defensive set-up is the reason why their complaints were justified.
Against Fulham last week, United had seven first-half corners and, from the last of which, they put together the type of move which, with Liverpool likely to react in the same way as Fulham did, they could seek to exploit tomorrow.
As Young plays the short corner to Juan Mata, Jesse Lingard is unmarked at the edge of the box and, as the ball reaches him (Figure 6), Fulham completely vacate the area in front of their goal in much the same manner as Liverpool in Figure 3, where the focus is on clearing the box rather than on marking players.
Once Mata keeps himself onside, Lingard has a relatively simple pass down the line and as Mata gains possession, he has three options in front of the goal, all of whom are unmarked because the defence has pushed out.
With Mata on the ball, all are now onside and even in his current form, Romelu Lukaku couldn't miss.
At the time of Mitrovic's disallowed goal last month, Liverpool were drawing 0-0, the same score as they were against Arsenal, Burnley and Everton when, this time from free-kicks from the left, they were perilously close to falling behind.
Just like from corners, Klopp's creative solution is a high defensive line but, unlike Manchester City who tend to drop back just as the ball is struck, Liverpool hold their positions, attempt to block runs and trust that their opponents will run offside and the referee's assistant will spot it.
Against Burnley, from Robbie Brady's free-kick (Figure 7), Barnes fired a volley past Alisson but was, correctly, judged offside. The potential issue for LIverpool is that Barnes' team-mate Chris Wood (circled), who is standing right behind him, wasn't offside and could just as easily have got on the end of Brady's free-kick.
Just like against Fulham, Liverpool spun the roulette wheel and it came up red.
Arsenal tried a different tactic from the same position where, to negate Liverpool's line, they played the ball short and moved it forward before crossing deep for Shkodran Mustafi to head the ball back across goal and Alexandre Lacazette to score.
Mustafi (circled, Figure 8), however, was one step offside and, once again, Liverpool trusted good judgement but good luck too.
Against Everton, again from a free-kick on the left flank, it was entirely the latter option.
Like Arsenal, Everton sought to create doubt as to where the free-kick was coming from as the right-footed Gylfi Sigurdsson placed the ball and, immediately, left-footed Lucas Digne crossed it as Liverpool held the line on the box.
However, both Theo Walcott and Yerry Mina easily broke the line with runs from deep but, Everton let them off the hook when Mina headed wide from seven yards.
Beside him, Walcott is also completely unmarked (Figure 9) and the defence has the type of disjointed shape which would have a large 'X' on it in any coaching manual on defending set-pieces.
It is, of course, Alisson's job to save shots - just as it is the assistant referee's job to spot offside - but by handing over responsibility to both when they are defending, Liverpool risk the likes of United or teams that wouldn't live with them in general play, taking an opportunity to alter the course of the game just as it could have done against Fulham, Burnley, Arsenal or Everton.
It seems churlish to question the team with the best defensive record in the league but, if United can prevent Liverpool from scoring at Anfield - as they have since 2015 - they'll almost certainly get a set-piece which, in the absence of any free-flowing football from United, provides them with the best chance to score.
The question, unlike most of Liverpool's opponents this season, is can they take it?