Before the World Cup Arsenal's defensive superpower had been their solidity when a dead ball flew into the box. Only two goals were conceded from set plays, one a Douglas Luiz corner that Aaron Ramsdale might well argue should have been disallowed for the vice grip in which Boubacar Kamara held him in. Every once in a while a giant such as Luuk De Jong is going to rise too high for anyone to defend but the Gunners were exceptional at winning the first header and blocking out opposition runners.
That has changed in emphatic fashion since 2023 dawned. Goncalo Inacio's unmarked header in the 34th minute was the fourth goal from corners that Arsenal have conceded since the start of the year to go with the wide free kick from which Brentford earned a point at the Emirates Stadium last month. The Gunners drew Sporting 2-2 in their Europa League round of 16 first leg.
One might make the case that the answer to this is little more than statistical variance, that no one can keep their set play defense under lockdown as Mikel Arteta's side did in the early months of the season. Heck, sometimes you just run into a collection of very tall footballers wearing the colors of Everton and Brentford.
However, the chances that Arsenal's opponents have been getting over the last two and a half months have been far more presentable. In that first period of the season, the Gunners gave up 0.18 expected goals (xG) per game off set plays. Since Christmas, that number has rocketed up to 0.34. Opponents are not necessarily creating a greater volume of opportunities but they are getting the sort of can't-miss headers that Arsenal were so good at taking away in the early months of the season.
The easy answer to this would be to turn to the set piece coach, Nicolas Jover, and ask what he has done wrong. And yet there is precious little about what Arsenal are doing at the other end to suggest that this is the result of bad coaching. There has been no commensurate drop off on the Gunners' own dead ball xG, which has gone from 0.41 to 0.37, and indeed an array of short corners have already been deployed to impressive effect, most notably through Oleksandr Zinchenko's strike against Aston Villa.
There is no one clear-cut explanation for Arsenal's set-piece difficulties but patterns have emerged. In particular, a look at where opponents are creating chances from would suggest that there is something of an issue that the Gunners have with deliveries from wide on the right, just slightly deeper than the penalty area, many of which are being hung up towards the back post.
Another consistent issue of late in Bournemouth's second goal on Saturday, Arsenal can be undone by screen and pick setting of the kind that Jack Stephens and Dominic Solanke set to give Marcos Senesi an unobstructed path to goal.
The Gunners tend to operate a hybrid between zonal and man-to-man systems, the exact makeup of which will vary in line with the opposition. On this particular set piece, Thomas Partey acts like a man who has been clearly assigned to guard Senesi but fails to battle through the bodies. Arsenal's other two defenders are tied to their men and it is ultimately an unobstructed header that takes Bournemouth, who have proven all season that they are an imaginative opponent from dead balls, two goals clear.
Earlier in the year Manchester United had applied the double screen to block Aaron Ramsdale's path as he goes to punch the ball. That goal is a reminder that small sample sizes can be distorted by sheer chance. What other explanation is there for the diminutive Lisandro Martinez's diving header that looped into the Emirates Stadium net?
Sometimes you cannot blame Arsenal all that much. There is only so much Martin Odegaard can do when matched up with James Tarkowski. Everton bullied the Gunners in the air because Sean Dyche has a team of very tall footballers. Sometimes it all comes down to individual errors. Whether Leandro Trossard was supposed to follow Ivan Toney when he peeled away for Brentford's equalizer, only Arsenal know. But if that was not the plan Gabriel and Oleksandr Zinchenko certainly did nothing to cover the Arsenal back post.
The goal that Brentford scored might ultimately have stood only because VAR forgot to draw the lines on that would have ruled Christian Norgaard to have been offside, but when Trossard went one way and Toney the other, it began a sequence where Arsenal players consistently lost their individual duels in the air.
Perhaps the simplest explanation is the most convincing here, that the end of the more settled side that Arsenal had between August and late January has brought a little more confusion to dead ball defense. One could say the same of Sporting's equalizer at the Estadio Jose Alvalade Thursday, where players who rarely feature made critical individual errors. As former England international Rachel Brown-Finnis noted on BT Sport, U.S. men's national team goalkeeper Matt Turner failed to defend his penalty area with authority when the corner came in from the right. "Turner has to come out and clatter everyone and clear the ball," she added. "He hasn't done anything to make his defenders feel confident.
"It's an inswinger, you've got to come and use the pace of the ball to get something on it. As a goalkeeper, you've got to command the area."
He was not alone in handing Inacio an all too easy opportunity to draw Sporting level after William Saliba's opener from similarly sloppy set-piece defending. Gabriel Martinelli had the center back in his clutches but let him slip away all too easily. Jakub Kiwior's efforts to clear the ball amounted to little more than a shrug as the cross flew towards him. Had it not been for the hash made of the corner, this game might have gone rather differently. Sporting had been putting Arsenal under pressure. But for most of this contest, the visitors were in the ascendancy, dominating possession and leading the battle for shots.
Sporting made the most of the chances Arsenal gave them to hit the sucker punch, a strong start to the second half undone by Paulinho on the break. It says everything of the fortitude of Arteta's side that they were not blown off course at 2-1 down, the effervescent Gabriel Martinelli denied only by a last-man sliding tackle by Jeremiah St. Juste after carrying the ball from his own third of the pitch, beating three defenders and rounding Antonio Adan. If there were any justice that would have stood as Arsenal's goal rather than the Granit Xhaka through ball that spooned off Hidemasa Morita.
Arsenal remains firmly in the tie but the errors they make and the goals they score on nights like this one are scarcely about the Europa League. This is a team hell-bent on lifting the 19-year weight of expectations to be crowned the best in England. Their set-piece defense has already cost them points that would have extended their lead over Manchester City. Jover, Arteta and his players will need to address this swiftly or it may cost them on far more important occasions than this.