They score a lot of low % chances
It's not uncommon to see teams, mostly good teams outperform their xG; this can be down to coaching and or overall quality of the players who take the chance.
However, as is mentioned in the book Football Hackers, there's generally not a massive deviation regardless of a players quality.
Omar Chaudhuri a data analyst, studied Cristiano Ronaldo's shots between 2010 and 2017 and observed that even with Ronaldo's undeniable talents he was only exceeding his non-penalty xG numbers ever so slightly. In short, Ronaldo was scoring on average scoring around two more goals per season than was expected of him.
With this in mind I think it's important to pay attention to teams that are massively outperforming their xG as regressions tend to be common.
How do we know if a team is outperforming their expected goals?
To calculate this, we take their goals scored and minus their xG. This will give us an indication as to which team is overperforming.
Looking at last seasons Premier League table we can see that Liverpool exceeded their expected goals tally by +12.3 goals, In the 18/19 season they overperformed their xG number again scoring +12.6 more than expected and in the 17/18 season they scored +11.6 more than their expected number.
Will we see a regression this season? Possibly. Klopp knows better than anyone the pain of this, In his final year with Dortmund he almost got the club relegated. Coming in from the Christmas break Dortmund sat 17th in the league.
Dortmund's underlying metrics (xG, xGA) weren't that bad they just experienced some terribly bad luck at both ends of the pitch.
Conceding a high % chances
I believe xGA(expected goals against) is a lot more predictive than just looking at the goals a team concedes.
Sheffield Utd are a good example from last season, they overperformed their xGA more than any other team in the Premier League last season. They conceded just 39 goals but their xGA indicates that 52.04 would have been more accurate.
How did they do this? A combination of heroic goalkeeping (Dean Henderson was excellent) and good luck definitely played a part
Looking at the games last season that went heavily in their favour were the games against Chelsea, the 3-1 win over Spurs (1.25-1.3xG) their win over Arsenal (0.92-0.77xG) and their win over Everton (0.21-1.36xG)
Looking at how a team has overperformed in this fashion can help us understand if their performances are sustainable. In my opinion Sheff Utd will probably regress this season if their underlying metrics are similar.
Strength of schedule
Bookies and the Public can often overestimate teams after a blowout win or two but it’s important to look at the schedule that the teams have been playing.
Let’s look at RB Leipzig from last season. On November 2nd they hammered Mainz 8-0 then went on a streak beating Hertha 4-2, Koln 4-1 Paderborn 3-2 Hoffenheim 3-1 and Fortuna Düsseldorf 3-0
Their next match was against Borussia Dortmund away and the market, in my opinion, had overestimated their chances. RB Leipzig opened on Pinnacle at 3.56 and got steamed into 3.07 before the game started.
The game finished 3-3 but Dortmund were the far better side and it was two individual errors that cost them the win.
Did the market over value RB Leipzig because of the results over lesser teams? I believe it skewed the probability.
What I find useful when evaluating teams is to see how they perform against similar strength opponents.
FootballFormLabs is useful for this as you can filter how a team performs against Top 6, Bottom 6, mid-tier, top half, bottom half etc.
TV Pundits are some of the worst analysts of the game. They can often over or underestimate teams because at the end of the day their job is to try and divide opinion and get people talking. Personally I don’t pay attention to commentary when analysing a game nor do I pay attention to TV/Radio pundits.
Public opinion / History
The Public opinion of some teams is enough to influence their betting trends. For example, Dortmund have developed a reputation that everyone is aware of. They are dangerous in attack and fragile in defence. This often means bettors default to betting the over and BTTS.
For years Juventus were the side that were responsible defensively and could grind out wins (not anymore). Slowly the markets are waking up to this but it took time.
Often people will maintain these opinions throughout seasons even without watching the team in question or studying their results more closely. This can especially be a pitfall when a team changes coach and they opt for different tactics.
It can take time for Bookmakers to adjust to this change. A perfect example of this was last season with Juventus. Juventus sacked Allegri who for the most part had Juventus playing as a defensive power house in Europe and a replaced him with what they had hoped would be a more attacking attractive style of football.
Betting markets didn’t massively adjust, Juventus had one of their poorest defensive campaigns in over a decade and myself plus my members enjoyed fading the Bianconeri throughout the season