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Kasey Keller vs. The Math

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As I had indicated on a recent gameblog at www.soundersfc.com I thought I would look at the numbers that we could expect from Keller in his first MLS season, and how much influence the defense would have on it.

There's going to be some heavy lifting after the break, as I'm confused as to which stats may or may not matter, and how to make the adjustments for the leagues and quality of defenses with in each league.

My initial estimate is that Keller if he is just in front of an average MLS defense for 25 games and normalized to the MLS average he will allow 54 goals, basically average. If Keller's talent stays stable to the EPL but has an average MLS defensive club in front of him we are talking about allowing only 27 goals in 25 matches. If the Sounders defense is bad, but Keller maintains form the numbers look to be 31 goals in 25 matches which would be a top 8 MLS keeper.

Same numbers over 30 games in the same order are 64, 32, 33.

First what do we know about Keller at Fulham last year?
He played 14 matches, faced 101 shots on goal (using saves+goals) and saved 83 of them allowing 1.29 Goals per game.

What do we know about the average regular (min 10 matches played) MLS keeper last year?
24 matches, 118 shots on goal, saving 86 of those and allowing 1.36 goals per game.

What do we know about the average regular EPL keeper from their last season?
31 matches, 179 shots on goals, saving 151 to allow 0.70 goals per game

From running these numbers I have found that there is a correlation between Saves to Goal ratio and Goals Against Average of .78 for MLS and .85 for the EPL. This basically means that a good Save to Goal ratio in the EPL is more likely to indicate a good GAA result. Also, the average EPL team gave up 5.73 shots on goal, where as the average MLS team gave up 5.02 shots on goal.

Here's where we get into some heavier lifting.

Since the correlation between saves and GAA is fairly good I what I have done is taken the MLS SOG rate divide Keller's EPL Save Rate multiplied by the EPL save rate (normalizing for his performance in EPL) and multiply by the games played. This is assuming that Keller performs as poorly to the MLS average as he did to the EPL average.

Similarly I used Keller's save rate without the EPL to MLS adjustment, but for the lower Shot on Goal average to establish his ability to block the lower shot rates. For the last number I used the Keller rate, but a higher shot on goal average of the EPL, but assuming that Keller's talent remains stable.

To put this in perspective, if van der Sar come over to MLS and played 25 matches he would allow 10 goals in 25 matches. I think we could agree that vdS would be a record setter in MLS, but that a few goals would sneak by him, as no one is perfect.