Expected goals: MLS leaders in 2021 and the key takeaways

As we enter the final third of the 2021 MLS season, we've reached the point where the sample size is plenty large enough that underlying numbers can paint a pretty solid picture of where things actually stand.

That applies to expected goals (xG), one of the foremost ways to measure the quality of a created chance and the likelihood that an opportunity will be scored. The chances are measured on a scale from 0-1, with 0 representing an opportunity that would be impossible to score and 1 representing a chance that should produce a goal every time.

Of course, xG doesn't always unfold in the real world. That's why there's some deviation from the Golden Boot presented by Audi race, with woodwork hit, flubbed chances, defensive blocks and more changing attackers' actual goals scored output.

With that framework, here are the top 20 leaders for xG for the 2021 MLS season as we approach Week 23. We've also included goals scored for comparison's sake, with the deeper data coming from Stats Perform. Seven key takeaways follow the table.

As strong of a season as New York City FC forward Valentin Castellanos is having, he's actually underperforming his xG by over six goals (6.07, to be precise). If the 22-year-old Argentine was a bit sharper in front of goal, he'd be the clear Golden Boot race leader.

Still, Castellanos' combined 16 goal contributions (10 goals, six assists) through 20 games are among the best in MLS. If he starts trending toward his lofty expectations, the Cityzens will have arguably the top striker in MLS – at least through a stats-driven lens.

Castellanos leads MLS in 16.07 xG, reinforcing the promising looks he finds atop Ronny Deila's deep attack. Now he's just got to capitalize on the chances – with more frequency – that the likes of Maxi Moralez and Jesus Medina create for him.

Sometimes stats can be deceiving, but Raul Ruidiaz's xG total (13.95) reflects that his Golden Boot lead is a true byproduct of the looks he's finding in and around the penalty area. The Seattle Sounders star has a league-leading 14 goals on the year, proving remarkably efficient for the Western Conference leaders.

The Peruvian forward already boasts a single-season high in goals scored since coming to MLS in 2018, but how high can he soar? With Nicolas Lodeiro back and putting opportunities on a platter, don't be surprised if Ruidiaz starts pushing 25 goals – or, at the very least, continuing to match his xG.

Another factor? Ruidiaz is also capable of popping up for an audacious and outrageous strike, much like his long-range chip against Austin FC from late July.

The only club with two players in the top 10 are the New England Revolution, who have a comfortable Eastern Conference lead and pace the Supporters' Shield hunt. Adam Buksa (13.64) is third in the xG table and Gustavo Bou (8.17) sits seventh, surely a byproduct of having MVP frontrunner Carles Gil (league-leading 15 assists, 75 key passes) setting them up to complete the club's Designated Player trio.

But Buksa, who's with Poland for World Cup Qualifiers in Europe, is actually underperforming his xG (13.64) by nearly four goals (10 total). The No. 9 has a penchant for hitting the woodwork (tied at six with Colorado's Cole Bassett for the league lead!) and has struggled to score against teams currently in the Audi MLS Cup Playoffs field.

The story flips with Bou, an MLS All-Star who's third in goals scored from beyond the box (3), trailing just Columbus free-kick wizard Lucas Zelarayan and Orlando City SC sniper Nani. Bou, with his left or right foot, seldom sees a shot that he wants to pass up. And those long-range shots tend to have lower xG values (8.17 xG; 12 overall).

Framing all this is that New England have scored a league-leading 44 goals this year. If Buksa starts trending closer to his xG and Bou stays red-hot, all as Gil returns from injury? There's danger brewing, surely.

Somewhat quietly, Sporting Kansas City forward Daniel Salloi is having an incredible year. He's been called into Hungary's squad for World Cup Qualifiers, made his first MLS All-Star Game presented by Target and has built a Landon Donovan MLS MVP case behind a league-leading 18 goal contributions (12 goals, six assists).

But is Salloi overperforming? Stats Perform's xG model hints at that, with Salloi's total clocking in at 8.73. To look at it from the other end, Salloi is beating the system to some degree and enjoying a career year that's making his downturn from the 2019-20 campaigns seem like a distant memory.

Should the SKC homegrown keep outpacing what xG predicts, his MVP candidacy will only strengthen. It also could push Sporting into the Western Conference's top spot for the second straight year, which would lock in home-field advantage to start the postseason.

A nagging calf injury has kept Javier "Chicharito" Hernandez out of more games than he's played during the 2021 season. Even still, his early-season form is good enough to put him ninth (7.97) in the xG table – and surpassing expectations at 10 goals (and one assist) through 10 games.

LA Galaxy head coach Greg Vanney hinted at Chicharito soon making his return after last weekend's El Trafico thriller. If Mexico's all-time leading scorer can compete and return to his goalscoring ways, he could surge up the xG and Golden Boot charts. And there's now a greater supporting cast around Chicharito, with the likes of Kevin Cabral and Dejan Joveljic finding success in their first MLS seasons.

Phrased another way: count Chicharito out at your own peril.

LAFC lead the league in underperforming their expected goal total (11.98) by nearly three goals, with only Minnesota United FC (9.19) trailing them in this undesirable spot. The xG model projects Bob Bradley's team to score 39.98 times, but they've only done so 28 times – contributing in large part to their current spot of 11th place in the Western Conference standings and 6W-9L-6D overall record.

As much as the Black & Gold – at least points-wise – have come short of expectations, some individual performances on the xG front are also at play. Diego Rossi (8.47 xG, 6 goals scored), who sits sixth in the xG table and is reportedly on the verge of joining Turkish side Fenerbache, hasn't quite met his 2020 form that procured the Golden Boot award. And the same goes for Carlos Vela (7.28 xG, 5 goals scored), who's battled injuries after encountering the same stops and starts endured a season ago.

If LAFC can start capitalizing on the ample chances they create, they certainly have the talent to return to the playoff mix.

Another striker in the xG top 10 chart who's overperforming his xG value is D.C. United's Ola Kamara. His 12 goals are tied for second in the Golden Boot race, though his xG sits at 9.04. For the Black-and-Red to continue their resurgence under new head coach Hernan Losada and hold onto an Eastern Conference playoff spot, they'll likely need the Norweigian sharpshooter to maintain these high levels.

On the flipside, Chicago Fire FC striker Robert Beric has regressed in front of goal this year – all after finishing second in the Golden Boot race during the pandemic-shortened 2020 campaign. The Slovenian DP has found net just three times, while xG puts him at 8.12. As much as defensive mistakes have hurt the Fire in 2021, Beric's cold shooting boots (and bout of bad luck) have played a role as well.