Back in 2014, I pitched a document I called “The Blueprint” to Brentford owner Matthew Benham. In that document were four pillars for style of play that when combined created a superior strategy for how to play football. These were based on significant research and analysis across a vast dataset of winning teams and the tactical traits they possessed. My hope was that The Blueprint would form the basis for a future style of play shared by Brentford and Midtjylland, and help guide successful player and coaching recruitment. One pillar of tactical style (obviously) involved Expected Goals. In attack, we want to create the largest volume of high xG shots possible. You can do this in various ways, but it boils down to creating shots from as close a range as possible, and mostly from central areas. In defense, you are faced with a few different choices. You can pick from a couple of varieties of aggressive pressing and attempt to limit shot volume, often at the expense of giving up good shots when opponents do break the press. [Yo, Liverpool.] Or you can concede game control, deep block, and let opponents take mostly bad shots from long range. [Examples: Arsenal. The Fighting Pulises] Or you can pick the Italian/Portugeuse middle block style where you cede the opponent’s half, but blow up everything central in your own half, and try to constrain both volume and quality at the same time. [Conte’s Chelsea, Mourinho’s Manchester United] I have my own preferences with regard to defensive scheme, but whatever you choose, it needs to successfully limit opposing xG somehow. Brentford are currently in 23rd place in the Championship, with 0 wins from 7 matches so far this season. This comes on the back of 5th, 9th, and 10th place finishes the three seasons prior to now. The narrative is that the Bees’ results have largely been caused by “bad luck”, so I thought it might be interesting to dig a bit deeper and see if that was the case. The Attack As I mentioned above, generating high quality shots was something we felt the team should focus on as far back as 2014. The coaching staff were made aware of this, and it was adopted as a core element in Brentford’s style of play moving forward. What was cool is that this actually seemed to work. Brentford’s open play xG per shot went from around 11% under Warbs in 14-15, and up to 12.2% under Dean Smith last season, which is very good for the Championship. Shots were generally getting closer to goal, and the attack was consistently very good. Then this season happened. Through 7 matches, Brentford are generating over 18 shots a game in attack. That’s excellent. But… Average xG per shot? A horrific 6.9%. That’s the second worst figure in the league next to Bolton, who somehow have a 5.5% xG per shot and look doomed already. And on average distance of shots from open play, Brentford are dead last at 20.4m a shot. Now as noted above, Benham owns two clubs. Here are Brentford and Midtjylland’s shots this season plotted side by side. (Note: BFC have played 7 matches, FCM have played 8.) That’s genuinely weird. Midtjylland are churning out amazing quality open play shots. Brentford have tons and tons of shots, but largely from range or wide, while the bulk of Midtjylland’s seem to be clustered around and even inside the six yard box. FCM take fewer shots – only 13.25 compared to Brentford’s 18.14 – but the quality difference is so vast that they could take half the shots BFC do and still post slightly better xG numbers. [Note: The numbers in the shot map differ from the numbers stated in the text above because each shot that is part of the maps is granular, whereas the stated numbers are part of calculated values that include possession chains. The chain numbers are more correct, but the maps represent unique shot values and not end-result possession values. These are more likely to differ from one another early in the season. ANYWAY…] The xG distribution charts make the differences even more stark. In basketball terms, this usually gets analysed as per possession efficiency. The Bees play a high-tempo, run-and-gun style but end up shooting almost exclusively long-range twos. The Defense Outside of Lee Carsley’s brief tenure as head coach, Brentford haven’t been a particularly good defensive team at any point since their promotion to The Championship. This year is by far their best performance at limiting opposition shots, solid 10.9 a game, but the quality on those shots is in the bottom 10% of the data set and tied for 4th worst in the league with fellow strugglers Birmingham. Now to be fair, Brentford are mid-table in xG conceded, which is solid. In fact, if Brentford were to match Midtjylland’s attacking numbers and keep their own defensive numbers, they’d be candidates for promotion. But despite the presence of Danish coach Thomas Frank on the coaching staff, it doesn’t seem likely that there will be a Voltron-esque merger of Danish attack and English defense any time soon. The real issue only becomes more apparent when you look at the numbers across both phases of play. The Variance Problem
- Brentford are currently taking a high volume of low quality shots in attack.
- They are also conceding a moderate volume of high quality shots in defense.
It’s a mathsy concept, but these two combine to form a toxic variance cocktail that makes poor results more likely to occur. This goes back to a piece Danny Page wrote in 2015 discussing distributions from various quality shots. In the example of Team Coin vs Team Die, two teams create identical xG numbers per game. However, because they differ greatly in quality, they will end up with different point expectations throughout the season. If you had make a choice, you would prefer to create fewer, top quality chances than many low quality chances because the variance in the latter would potentially yield fewer points in the league table throughout a season. In nerd terms, Brentford are practically rolling a 16-sided die right now when they shoot. Their opponents get to roll a D8. That’s not a healthy situation. This problem is further exacerbated when you realise that most of the error in xG models is going to be at the extremes. If teams are taking a lot of long range chances against packed boxes, then those chances might actually be worse than the model thinks (and the model already thinks Brentford’s are bad). Conversely, if they are regularly giving up high quality chances, those chances might also be quite a bit better than the model’s already beefy assessment. Back to Brentford… Someone on a Brentford forum recently noted that even at Walsall, Dean Smith was considered a “streaky” manager. That’s certainly been true in his time at Brentford, where his teams have combined prolonged losing and winning streaks each season to eventually land mid-table. However, as shown above… there might be a reason for that. The best coaches implement tactics that help control for variance. They can’t eliminate it completely – football is a low-scoring, and inherently variable game. However, coaches that focus on the details and prepare their teams to handle them consistently seem to do better in the league table. For whatever reason, this season Brentford have embraced the opposite. They are highly variant on both sides of the ball right now, underperforming a lot in attack, and currently paying the price. Equally frustrating is despite a high pace and enormous shot volume, Brentford are near the bottom 5% of all teams in xG from set pieces. In a similar vein to the attacking shot maps above, it’s not as if Brentford don’t know about the value of set pieces. This was another one of the key pillars of playing style in The Blueprint document from 2014 and helped power Midtjylland to their first ever league title in 14-15. Unfortunately, as I’ve explained many times before, having useful knowledge and executing the concepts well are entirely different things, especially when it comes to football. At the end of the day, execution on and off the pitch is what really matters. Will Brentford Get Relegated? Looking at the broader numbers across the league, at this point it seems possible but also highly unlikely the Bees will go back to League One. Unlike Burton and Bolton, who already seem mostly doomed to be flushed from the Championship toilet bowl, Brentford are probably more deserving of a mid-table placement. This doesn’t mean they absolutely won’t be relegated – decent teams have been sent down from the Championship before – but with 39 games left, it’s fairly improbable. Hopefully the explanation above shows that the Bees aren’t entirely undeserving of the current plight either. Brentford’s outputs in attack and defense right now contain of high degree of variance, and are possibly even worse than most xG models expect them to be. Ironically, they also run counter to all the advice we gave them back when various members of StatsBomb were part of the Benham football project. Ted Knutson firstname.lastname@example.org @mixedknuts