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The math behind the inevitable LA Galaxy victory

Using shot data to analyze last Sundays game, and predict the outcome of the Western Conference Finals series between the LA Galaxy and Seattle Sounders.

Harry How/Getty Images

Last Sunday's match between the LA Galaxy and the Seattle Sounders was a nail biter. From a shot perspective, the game played out exactly as Harrison Crow, founder of American Soccer Analysis, predicted on our podcast. In said podcast, we talked a lot about the concept of expected goals and how advanced analytics is transforming the way we see the game.

Now this article deals heavily in the concept of expected goals, so if you are unfamiliar with the concept I recommend this article as a good layman's primer. For an even simpler primer, know this: Expected Goals/xG is a way of determining how many goals a team or player is expected to score given the location and circumstances of their shots.

As Harrison predicted, LA limited Seattle’s shots, but the shots they did give up were dangerous. Seattle gave up double the shots of LA, but most of them were from low percentage areas. Seattle, as Harrison predicted, could close the gap in terms of number of shots by way of generally taking more dangerous shots than LA-- and this is exactly what happened. Despite LA having double the amount of shots, the teams were nearly dead even on expected goals.

In terms of percentages Seattle took 3 of the top 4 shots on the night, with Dempsey's 20th minute shot (Gracias San Penedo) leading the way with a 60% expected chance of a goal. The other two came from Obafemi Martins and both had a little over 25% respectively. The best chance LA had all night came from Robbie Keane nearly 7 minutes in, a shot with a xG value of roughly 35%.

Humorously, LA's goal game from one of the worst chances on the night as Marcelo Sarvas' shot had an xG value of around 6%. Harrison Crow admired LA's approach of limiting shots, because when you allow as many low percentage shots as Seattle does eventually that's going to catch up to you. On the night, it did.  It also goes to something that I have long spoken about in terms of the Galaxy's attack.

For all the possession that LA is able to maintain, this is a team that likes to shoot a lot. They often score by sheer shot volume. In fact, they lead the league in shots. Sometimes they are high percentage, and sometimes they are low percentage. But even when they are low percentage, by merit of taking so many of them the xG odds start to accumulate; usually materializing in goals. It is a numerical brute force offense.

For a good analogy, think of soccer as a game of dice where rolling the die's highest value is equivalent of scoring a goal. In this game, there are two big factors that will affect your odds: 1) How many sides are on the die, 2) How many rolls you get. The number of rolls you get is equivalent to the number of shots you take, and the number of sides on the die is dependent on where and the conditions under which you are taking those shots.  [ed: Like Dungeons and Dragons!] LA's offense works by way of maximizing the number of rolls/shots. When teams are unable to keep LA from getting open looks in the box, i.e. RSL in the last series, LA will romp as they are getting 20 or so rolls at a die with very few faces.

The Sounders defense works by increasing the sides of the die, keeping teams from getting those open looks in the box.They do this by limiting the space between their lines, and compressing when teams get into the final third. They often concede space on wings, in order to get more players in and around the box.  The number of crosses LA sent in was 60% higher than that of their season average. This wasn't wing dominance. This was by Seattle's design. When you have a guy like Chad Marshall who wins a higher percentage of aerial duels than even Omar Gonzalez, you're more than happy to allow LA to send in cross after cross.

This allows Seattle to focus more on keeping teams out of high percentage shooting areas within the box. One way they do this is through their defensive mid; thus Alonso is so important to this team. He stops teams from playing those one and two touch combinations when entering the box that usually neutralize such a defense, turning defenders into cones. Although Alonso was injured on the night, Azira stepped up in a major way. As Mathew Doyle pointed out in his article, Azira was so stone cold focused on sitting back and disrupting that he only completed 4 passes in the attacking half of the field all game. That's precisely how you force a team to go wide, as LA did.

Seattle's focus on packing the penalty area definitely shows itself in the stats. 40% of LA's shots were outside the penalty area. LA had 12 shots in the box, but only 1 was on target. 4 were blocked and the others were off target thanks to defensive pressure.

And here is an example of the strategy in action.

Seattle allows Ishizaki to go one on one with Pappa, effectively conceding the cross by having Azira and the fullback tucked in.  By doing so, they are able to put 5 men in the box and have Evans floating just outside the box, ghosting Keane, who is always one to step back in these situations to create space for himself. In fact, it's Evans who eventually recovers this ball.

So that's how Seattle defends, and as I mentioned, LA was able to overcome it through numerical brute force.  If we go back to our dice analogy, according to the data, Seattle limited LA to an average die roll of 10 sides. Their average shot only having a 10% chance of scoring. But LA did score, and they were very close to scoring another. This is because they had 20 shots. 20 rolls at a 10 sided die.

Ok, now let's flip the table and look at Seattle's offense. You're probably expecting some balance at this point and that I'll tell you that Seattle's offense works by maximizing limited shot opportunities, or in the die analogy, rolling dice with fewer faces. It would certainly make for good article structure, but it unfortunately does not play out in the numbers.

During the season, Seattle's average xG per shot is only slightly higher than LA's and they are actually tied for third in league in terms of total shots per game, not too far behind LA. It did however; play out on the night, and for one simple reason: 4 of their 5 best chances came from set pieces. Seattle had a 1.728 xG in the game, however, 73% of that sum came from corners, free kicks and throw ins. From open play, they were under half an expected goal.

So there you have it. LA has to tighten up its set piece defending. LA allowed Obafemi Martins a 60% chance when Robbie Rogers failed a headed clearance and instead headed it down to the feet of Obafemi Martins. The resulting rebound shot by Dempsey had 20% chance. That's over half of their xG on the night right there (gracias San Penedo). Mistakes like that can cost you a series, and LA was fortunate that Seattle did not grab an away goal in that instant. The good news, however, is they didn't, and set piece defending is something that Bruce will no doubt have the team working on. If LA can tighten that up, their smothering defense will put the odds well in their favor that Seattle cannot score 2 goals against them. LA heads into Seattle needing only a goal to cause full blown panic in Seattle via the away goals rule, and since Seattle's defense allows so many shots (although not from the best positions) mathematically LA is in great shape to get it via sheer volume as they did on Sunday.  Shots. Shots. Shots. That will be the key to a series victory for LA, and from a numbers standpoint, LA is in the driver's seat.