Converting Dangerous Passing into Shots
When watching the Milan-Torino film for my last piece, the idea came to me to look deeper into dangerous area passes. Torino had put the ball into dangerous spots a lot in the first half but a check of the shot map made their half look harmless when it had actually been anything but. That led to a lot of research and then into this post, where I'll look at how often passes into dangerous areas are converted into shots, the difference in assisted and unassisted shots, what teams do this well and poorly, and ask what we can do with all this new data. Hopefully you will find this as fascinating as I did.
What are dangerous, or Very Deep passes?
Passes played very deep into the opponents area.
Okay, smartass, what is this area you are defining as Very Deep?
The area roughly covered by blue lines here, within 15 yards of the opponents goal
Okay, what is so special about this area, I am tired of learning about new areas and terms why should I put this one in my memory bank?
To ease the understanding of the rest of the article. There is no special reason I chose exactly 15 other than it's a clear number. Teams converted 18% of shots from this area, compared to 6% in the 15-25 yard range but that is likely true for 14 or 16, but I chose 15. Very Deep is also easier to say that 0-15 yards of opposing goal every time.
How often do teams pass into this area?
I see where you are headed. To pre-empt the next few questions, here is a general table:
If you complete a pass in this area and get a shot off then unsurprisingly it is a golden chance. It follows that turning more of these passes into shots one of the best ways to improve your offense (or vice versa for defense).
A few quick best and worst lists to put down some context.
First, to explain the difference in the two right-most columns. Assisted shots/completion is how often a completed pass turns into a shot. Total shots/pass is all shots (assisted and unassisted divided by total passes into the area).
A couple interesting observations: Manchester United's soft underbelly shows up here, nearly the easiest to complete passes against in this area and then allow nearly the highest shots/pass of any team. Those are simply unacceptably bad rates for a team with their payroll. Dortmund allow the fewest completions per game, yet when they are completed they were converted into shots at the 4th highest rate. This makes me think there is very high pressure on the players attempting the pass and maybe higher risk defending on the recipient.
Ok, so where do passes into the very deep area generally come from?
(sides have been equalized to hopefully increase comprehension, differences not significant between sides, the huge box with 13 in it is the entire own half, opposition half is the rest broken down)
We see that passes into the Very Deep area come primarily from the sides, in a season an average team will play 350 passes from the corners of the pitch into this area (not counting actual corners).
All Very Deep passes aren't created equally are they?
No they are not. Here is how often they are converted directly into assisted shots:
So we see that as we expected it's better to play a shorter pass from the middle of the field into the area than to hoof one from out wide. Only 1 out of 29 passes from the corners turns into a assisted shot while 1 out of 8 from the middle outside the box turn into assisted shots.
That's a European average though, does it mask differences from league to league?
As you'd suspect looking at the leaders charts above, it absolutely does. Let's look at the Bundesliga vs Ligue 1:
We see that long passes from the sides of the pitch are turned into shots over two times as often in Germany as they are in France. This variation in styles between leagues (which also shows up in shots) is one of the more interesting questions in football data. Teams in the Bundesliga press out a lot more than in Ligue 1, leading to some of the differences we see here and causing pesky problems for anyone trying to build any sort of expected goals (or, as I briefly and madly considered, expected shots *shudders*) model that covers more than one league. Pressure is the missing component I assume, as there are simply fewer defenders covering pass recipients in the Bundesliga than there are in France but until we can account for that, differences in playing styles across teams leagues will continue to trouble global model-makers, in which I semi-proudly claim membership.
A few interesting team maps before we move on, first Barcelona. Barcelona attempts passes from the deep sides of the pitch near the halfway line less than any other team in Europe. They tried only 6 passes from there, understandably working the ball through the center.
Mainz on the other hand tried 47 passes from the sides near the halfway line:
Dortmund rarely allowed any dangerous passes, though as we saw the very few that were completed caused major damage.
while Swansea allowed 139 passes that originated inside the box (which led Europe):
I know you just disregarded an Expected Shots model but let's see it in action anyway.
If you insist, and at the least it leads us to some interesting conclusions even if it is simply an assisted shots model. It is a very simple setup: if a pass came from the center square it is given a 12.5% chance of leading to an assisted shot, from the corners: 3.5%, etc, etc. You can look back a few graphs up at the % of Very Deep passes leading directly to shots graph to see the rest. Looking at actual shots compared to "expected" shots will tell us who was the best offense at turning dangerous pass attempts into very dangerous shot attempts and who was the best defense at defusing their box being bombarded by limiting the number of shots.
As expected we see a lot of German teams are great at converting their passes into shots above the rate we would expect based on where those passes came from, starting with Wolfsburg who took 32 more assisted, close-range shots than we would expect from their pass numbers:
So if Athletic could convert passes into shots like Real Madrid, they would have added 50 more assisted shots to their total. If they converted those at the European average rate of 40%, they would have scored 20 more goals and possibly threatened for Champions League. I think that this means Athletic's attacking line is holding back a team with the potential to easily score 50+ goals. They have enough dangerous possession to be doing much better, so if looking for an offensive upgrade I'd look toward those involved in the final ball as the players behind them are being let down by those in front.
Looking at defenses I will split it up by league so it's not just a list of German teams in the top 10 of defenses who allow a high rate of shot conversion (number is "extra" shots allowed above or below what would be expected from pass totals and origin):
Here we see possibly why Sunderland stayed up this season. They are a surprising name to see on the left side of this table and facing 12 fewer high quality chances than expected was a big boost toward gaining the 3 key points between survival and the Championship.
We can look deeper into each league with the following images and interactive links. In Germany high on the y-axis Bayern and Dortmund are the teams well ahead of the pack in sending passes into the box. Gladbach's extreme efficiency shows up as they are near the bottom of Very Deep passes attempted, but they are best in the league in converting passes into shots. The dark color of their circle shows it's not just passes from high quality areas, they are simply converting passes into shots at a rate above anyone else in the league. The size of the circle shows they are converting those shots into goals atop the league as well.
In the EPL we have more uniform conversion rates outside of Man City.
In La Liga we see massive spreads in conversion rate and very deep passes per game. This wide spread has always made this league the toughest to model correctly.
La Liga Offense
An interesting case is Serie A's defenses. 6 teams allow essentially the same amount of passes into the box but we see the difference in Juve, Lazio and Roma (the top 3 teams in the table and fewest goals allowed) is they turn those passes into fewer shots allowed than Inter, Fiorentina and Napoli.
Serie A Defense
Looking one step back
What about the yellow area (15-25 yards out from goal)? It's not near as dangerous: only 22% of completions turn into assisted shots and 10% of assisted shots are turned into goals (Unassisted shots clock in at 3%). There are still interesting things to learn looking at this area. I looked at the ratio of completions in the yellow area (deep) to the blue area (very deep), thinking teams that build a shell around their goal might keep the action at arms length.
We see a familiar face at the top in Chelsea. Mourinho's wall around the goal is a familiar, frustrating sight for EPL teams and it's borne out here. You can get close, but not close enough to get a really high quality shot.
At the other end Leverkusen tries to not let teams get close to their goal, but when they do they don't slow down on the doorstep they barrel down on goal. Teams who have a high completion ratio (like Chelsea and Everton) are also generally better at keeping their opponents from converting passes to shots. On offense that relationship does not hold, though Chelsea and Everton are again near the top.
The offensive top 10s look like this:
What are the uses?
These metrics can help evaluate where your team's attack or defense is being let down. We used Dortmund's defense earlier and identified the final link as the weakest: they are allowing an extremely low amount of very deep passes and a low completion rate, but those completions turn into shots way too often. If they can get that rate down to even European average, that could be 35 fewer shots they would face. It gives us a glance at where teams are entering the ball to dangerous spots and how well they are converting those passes.
What is missing and what is the next step?
The obvious next step is looking at which of these metrics are repeatable and which are most influenced by luck. Right now, I have no statistical backing to say which is which but I am pretty confident that simply based on larger sample size, pass-to-shot conversion rates are much more indicative of true skill than shot-to-goal conversion rates.
Applying these metrics to individual players would be an interesting use. If Leighton Baines crosses are converted into shots at a significantly higher level than everyone else that is useful information. Same with strikers, if Aubemayang is converting passes into shots at an elevated rate while Ramos and Immobile are not, then he might be the reason and not the supply. Defenders can be looked at as well, though as usual that comes with a lot of complexity.
Problems with these metrics are the difficulty in classifying unassisted shots. Some of these likely were assisted from passes just outside the area I selected as a cutoff but it is hard to determine which ones come from dribbles, loose balls, rebounds, etc. That would add useful information. It almost doesn't need to be stated at this point, but pressure would totally change how we look at metrics like these and shots. Without a huge manual project, it's unlikely we will have Europe-wide pressure stats anytime soon.
Of course, the ultimate end point is shots to goals but I felt the piece was already long enough and I don't have as much new to add in that area. There has already been plenty of good work (like this piece from Michael Caley) that has established a lot in that area. Classifying % of shots taken as headers from each area would be another improvement I could make.
Thanks for sticking with this piece through the stats and the tables. Hopefully you enjoyed it or it sparked an idea for you. If you have comments, critiques, ideas, or anything else you can reach me @SaturdayonCouch on twitter or you can post a comment on my website.
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