How quickly can a club’s fortunes turn around? Swansea City finished eighth in the last English Premier League season, but quite a few statistics suggested they benefited from luck. So much luck, in fact, that a few months ago I tweeted something rather pejorative about the team:

Now, you don’t have to be an analytics expert to see why I tweeted this. Just look at the table:

No team above Swansea had a negative goal difference, and Swansea’s goal difference was the same as West Ham’s, down in 12th place. In contrast with the Hammers, Swansea got their goals at exactly the right times, racking up nine more points over the course of the season. That’s probably not repeatable.

Look a little deeper, and more problems become apparent. Swansea ranked 17th overall in terms of shots taken – 20th for shots from corners, 17th for shots from set pieces, and 14th for shots from open play. They were 15th for shots allowed. In terms of shots on target – a pretty reliable bellwether for overall performance – Swansea ranked 14th in shots for, joint 16th in shots against, and 16th for the difference between the two. This was hardly a dominant team.

Luck came at the end of a player’s boot, too. Eight of Swansea’s 46 goals came from Ki Sung-Yueng, who took only 28 shots. That’s a conversion rate 11 percentage points higher than Sergio Agüero’s, and Ki typically shot from a greater distance. Swansea also benefited from three own goals, which are notoriously random; only Liverpool and Southampton had more.

These were not the numbers of a team that would consistently finish eighth, and I haven’t even mentioned fancy stats like expected goals. As I said in my tweet, if Swansea continued in this vein, bad things would probably happen. But they didn’t continue in this vein at all!

So far this year, the Swans rank third in shots on target for, second in shots on target against, and third for the difference. The team is simply performing at a different level. A big reason is the presence of André Ayew, signed a few days after my fateful tweet from Olympique de Marseille. He’s been directly involved in every single one of Swansea’s six goals from open play: three goals, one assist, and two “hockey assists” (passes before the assist).

The Swans have also benefited from the services of Jefferson Montero, one of my Premier League hidden gems, in three of their four matches to date. He’s prone to injury, though, having played fewer than 1,700 minutes last term. The big injury worry, of course, is Ayew – he’s had a couple of long layoffs in the past several years, and losing him for a few months would put a big dent in Swansea’s hopes for the season.

But there’s something else going on that’s more systemic. As readers of this blog know, I have expected goals models based on shot creation and ball progression. Together, they can be used to measure a team’s efficiency. Last season, the Swans operated at par when attacking, creating as many shots as you’d expect given how well they advanced the ball. But they were especially effective in defense, conceding only about four expected goals worth of shots for every five you’d expect, given teams’ penetration of their half.

This season, the Swans are advancing the ball more – enough to raise their goal total by a quarter, in fact – and creating even more shots than you’d expect based on this ball progression. But it’s their defense that steals the show. They still allow opponents to penetrate deep enough to score more than a goal a game, but the shots they’ve ended up allowing would have been expected to result in only half as many goals. That’s a devastatingly efficient defense, much moreso even than last season’s. And the same four defenders and goalkeeper, including new boy Kyle Naughton, have played every minute of every game so far.

Swansea’s defensive numbers are not unprecedented – a few of the usual top clubs produce them as well – but they may represent an enormous change in the team’s effectiveness. Together with a boosted attack, the club is putting up numbers that would have been unrecognizable last season. If the Swans can keep it up, they’ll be able to finish even higher up the table. So what’s behind this revolution? Just personnel changes, or actual tactical innovations? That’s going to remain between me, the computer, the video monitor, and Garry Monk. But the message, at least whatever message there is through just four matches, is clear: This isn’t last season’s Swansea.