The rise of the underlap

Imagine you’re Andrew Robertson in the Merseyside derby and you see Sadio Mane up ahead about to gather a loose ball at the corner of the box and dribble at the defence.

You’ve got a quick decision to make.

One thing you could do is hang back and let Mane try to beat his man one-on-one. After all, you’re nominally a defender, and if Liverpool lose the ball someone will have to stop Andros Townsend and Richarlison from counter-attacking up your flank.

Then again, you’re a full-back in a modern back four, and everyone knows the job is as much about getting forward to help the attack as it is about defending. The textbook thing to do here would be to swing around the outside of Mane on an overlapping run. If he slides you the ball at the right moment, you’ll be in behind the back line with space to look for a cross.

But there’s also a third option: instead of sweeping around the outside, what if you cut inside, into the channel between the opposing full-back and centre-back? The angles on this so-called underlapping run are more difficult than an overlap for the passer and the receiver, but if it works it can create all kinds of headaches for the defence.

Last week, Robertson took the road less travelled, pointing to where he wanted the ball and underlapping behind Everton right-back Seamus Coleman. It left Coleman no chance to switch on to the run.

The nearest centre-back Ben Godfrey was reluctant to leave his partner Michael Keane alone with Diogo Jota, and by the time he closed down Robertson near the byline, the Liverpool left-back had already stepped around Mane’s pass and cut the ball back to a wide-open Jordan Henderson…

… who curled a shot past Jordan Pickford from the edge of the penalty area.

Start your day with the beautiful @JHenderson strike that got things going at Goodison 😀 pic.twitter.com/pHEbRsY8Xv

— Liverpool FC (@LFC) December 2, 2021

The underlap felt like an inspired bit of improvisation from Robertson, but it was part of a larger shift in Premier League tactics. Over the past six seasons, attacking full-backs have increasingly varied their positioning and movement, overlapping less automatically than they used to and underlapping more often.

If you’ve noticed the trend of full-backs attacking inside, it’s not just your imagination. Data can not only help track the league-wide change over time — it can also give us some ideas why it might be happening.

The statistical rise of full-back underlaps

The tricky part about measuring overlaps and underlaps is that event data logs where things like passes and dribbles happen but cannot tell you how players are moving off the ball. To infer what kind of runs full-backs are making, you need to know not only where they are taking their touches but how the ball got there.

The quintessential attacking full-back run happens in a situation similar to the Mane and Robertson example above. Overlaps and underlaps can be useful in lots of other ways, but they’re most common when an attacker has the ball somewhere around the corner of the box and needs a team-mate in support to help overload the defence.

For measurement purposes, if a team-mate in the half-space near the corner of the box passes at least five yards to a full-back on the wing, we’ll label that an overlap. If the players are the other way around, that’s an underlap. This won’t capture every full-back run, but will narrow it down to passages of play where the data gives us a relatively clear idea of how players are interacting on the pitch.

If we compare overlapping and underlapping plays to each other, there’s a noticeable historical trend. For the first half of the last decade, full-back overlaps made up around 90 per cent of the combined set of passes. Wingers and midfielders were passing from the inside out to full-backs who advanced almost exclusively up the sideline.

But ever since overlapping peaked in the Premier League in 2014-15, underlaps have been on the rise. Last season, 17.5 per cent of the full-back moves in this set of passes were underlaps, up from 9.5 per cent seven years ago. It’s still relatively uncommon for a full-back to come inside in the final third to receive a pass from a wider team-mate, but there’s a lot more variety than there used to be.

To get a better handle on how and why this part of the game is changing, it’s worth taking a closer look at four different kinds of full-back moves.

Diagonal overlaps

It’s not actually the most common, but maybe the most iconic of our four pass types is the diagonal pass to an overlapping full-back. It came into vogue in the last couple of decades thanks to the rise of the 4-2-3-1 formation and inverted wingers who like to play narrow and dribble in to shoot on goal. Fast full-backs could time their runs up the open wings to receive an easy lay-off pass from a winger or midfielder for a cross.

Tottenham’s lone goal against Arsenal in September doesn’t come off cleanly but the crisp timing of Sergio Reguilon’s overlapping run and Bryan Gil’s valiant attempt at a one-touch relay point to a team that have practised this wide pattern in training.

In fact, Spurs stand out as one of the few big clubs whose tactics have cut against the league trend, with overlaps on the rise and underlaps declining under Mauricio Pochettino, and rebounding only slightly since.

Tottenham’s conventional full-back play has its advantages — Reguilon leads the team for expected assists — but if you can imagine how exposed they would have been if Bukayo Saka had recovered the loose ball here and launched a counter-attack up the wing behind Reguilon, you’ll see why these swashbuckling overlaps aren’t as popular as they used to be.

Out of 4,808 completed diagonal passes to overlapping full-backs in our custom dataset, only 84 have produced goals for the attack on that possession, a rate of 1.7 per cent. On the other hand, 12.2 per cent of those passes have been followed within the next 15 seconds by a counter-attack that reached the opposing half on the flank of the full-back who overlapped.

Even if you’re good at it, sending a defender all the way up the wing is risky business.

Lateral overlaps

Of course, an overlapping full-back doesn’t have to sprint all the way to the corner flag. Sideways passes from the half-space to a wide full-back are more than twice as common as completed passes of the diagonal kind.

These lateral overlaps are the least threatening of our four pass types, producing a goal from the sequence only 1.2 per cent of the time. They’re less a dynamic threat than a simple way to provide consistent width outside of narrow wingers. But full-backs in these positions can still stretch the defence in useful ways, as Diogo Dalot showed last weekend against Crystal Palace.

The decisive moment in #MUNCRY, courtesy of @Fred08Oficial! ⚽#MUFC

— Manchester United (@ManUtd) December 5, 2021

Lateral overlaps are slightly less likely to lead to a counter-attack up the flank behind the full-back, but they’re also 31 per cent less likely than diagonal overlaps to produce a goal — not an especially enticing trade-off.

Lateral underlaps

The growing alternative to overlaps is a narrow full-back working the half-space in the attacking third. Instead of committing a defender wide and high, where he’s not in a good position to counter-press or track back after a turnover, some coaches are experimenting with a return to using wingers for attacking width and tucking their full-backs inside.

Like a lot of tactics trend stories, this one has a lot to do with Pep Guardiola, who really, really likes wide wingers. If you’ve watched even a little bit of Manchester City lately, you have probably noticed the outsized attacking role Joao Cancelo has been playing inside the left winger.

But Guardiola’s tactic of stretching the back line early — by pushing a winger high and wide who then passes back inside to a full-back between the lines — isn’t exclusive to one player. Against Aston Villa, it was Oleksandr Zinchenko running up the left channel after a long ball to Raheem Sterling. As Villa’s defenders ran out to close down Sterling, Zinchenko received an easy lateral pass between the lines and tried his luck from distance.

Even if we leave out City, who do far more lateral full-back underlaps than any other team in the Premier League, this kind of outside-in pass produces a goal nearly as often as a diagonal full-back overlap, while leading to the fewest counter-attacks of any of our four pass types. An inside full-back can support the attack and stay in a good position for “rest defence” — a term for preparing to defend after a turnover while still in possession — at the same time.

Underlapping full-backs can produce a fun variety of attacking patterns. In Manchester United’s game against Leeds, for example, Luke Shaw beat his man-marker by passing up the wing to Bruno Fernandes and then cutting inside to take the return pass into the channel for a shot.

Or take this clever rotation from Crystal Palace against Newcastle. The right-back, Joel Ward, starts the play from deep with a pass out to Michael Olise on the wing (out of shot).

Instead of waiting for a full-back overlap, which would have taken too long, Conor Gallagher makes the inside-out seam run from midfield to give Olise a passing option up the touchline.

Ward runs straight up the channel into the vacated midfield space and first-times a ball out to Gallagher, and suddenly Palace have managed to achieve the effect of an overlapping run — a ball-carrier in space on the wing with time to pick out a good cross — with a more efficient pass-and-move pattern.

Diagonal underlaps

The last of our four full-back runs is the one we started with — Robertson’s sprint up the channel for a diagonal pass into the box from the wing. When they come off, passes into this prime cutback zone are deadly: a 2.9 per cent scoring rate from diagonal underlaps is nearly double that of any of the other three.

But these passes aren’t completed very often at all. Across the Premier League, only 13 diagonal passes have reached a full-back in the box this season. Those passes led to three shots and two goals, but they also produced counter-attacks at the highest rate of the four run-types. Maybe that trade-off is worth it for the higher scoring chance from the half-space, but it would take more advanced math (and a greater sample of completed passes) to find out for sure.

It’s also possible that these runs are effective even when they do not lead to a completed diagonal pass. In that Liverpool goal from the opening example, Coleman could have cut off the passing angle to Robertson by dropping off of Mane a step or two, but the difficulty of knowing exactly when to move to block a run behind his back might have opened space for Mane to cut inside, which isn’t exactly an ideal outcome for the defence either.

Unfortunately, that is probably beyond what event data can measure. Some of the tactics driving the rise in underlapping full-backs aren’t easy to track with numbers alone. But after all, isn’t being hard to track why they make the runs?

(Design: Sam Richardson)