Context is Important – But its just as Important not to OVEREMPHASIZE it.

One of the most frequent complaints “anti-analytics” people make about so-called advanced stats is that these stats fail to adjust for context – some players have harder minutes than others.  This complaint is of course bunk, and a complete straw man – analytics has come up with numerous methods on calculating how difficult a player’s minutes are: From measures of competition, to measures of teammates, to measures that contextualize where players start their shifts most often (zone starts) – we have multiple metrics to explain EACH of these things.  Sure you can use fancystats incorrectly and completely ignore context, but good analytics work doesn’t do that, and it’s pretty easy to see where someone is and isn’t attempting to take into account context.

That said, with the new season coming up, it’s important to remember not to go TOO FAR when doing this.  That is, context is important, but context doesn’t explain EVERYTHING.  And people often tend to forget this.

Take Quality of Competition for example.  Competition matters on a micro level.  If a player plays against a top opponent rather than a 4th line scrub, he’ll have a lot worse results.  See this Eric T chart below:

However, teams don’t really have great control over the opponents their skaters face, and the level of competition that each player faces over a span of games, and especially over a single season, tends to be pretty similar to every other skater.  Take the Isles last year for instance.  The top competition any Islander faced (Grabner) had an average of 51.5% corsi.  The Bottom competition?  50.2% (Cizikas).  The gap between 51.5% and 50.2% isn’t really big at all,

So while Quality of Competition (QOC) matters, over the long run, it basically doesn’t – as the differences in player competition are way too small to make a difference.

In other words:
1.  DO! Complain about Capuano (or any other coach) putting scrubs out against top liners at a crucial point in a game.
2.  DON’T! Expect over the long run for it to affect a player’s possession stats much at all.  It is NEVER an excuse for bad player possession over the long run.

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Similarly, take Zone Starts (the % of non-neutral zone faceoffs a player starts that are in the offensive zone).  Every additional Offensive zone faceoff that a player is on ice for increases his raw corsi by roughly .4 (and fenwick by .3).  Zone starts clearly matter, certainly more than quality of competition.

But gaps in player zone starts also aren’t THAT huge.  There are, unlike quality of competition, a few players throughout the league who do have really extreme zone starts – and for them adjusting is key.  But for most teams, zone start gaps really aren’t that huge.  Matt Martin for example, has had a zone start % about 8 percentage points lower than the Isles have with him off the ice the last two years.  That’s a big gap!  And yet, if you run the #s, that only lowers his relative corsi by 1 percentage point!  In other words, despite facing some of the rougher zone starts of any Islander the last two years, his possession numbers are only slightly affected.

So to sum:
1.  DO Take note of the Zone Starts players have, and you can certainly complain when Capuano randomly has Nielsen getting a lot of offensive zone starts the first few games of the season.
2.  DON’T argue that zone starts explain good or bad possession numbers – that nearly always isn’t true, except maybe in as few as 5 situations around the league where players are beyond buried in the D Zone (Capuano never does this, so you don’t need to worry about it with the Isles).

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This isn’t to say that all contextual stats don’t matter that much – Teammate strength (Quality of Teammates aka QOT) matters a LOT!  It’s a bit harder to measure though due to sample size issues – one method of measuring it (used by BehindtheNet and War On Ice) includes data of teammates when they are WITH the player whose QOT you are measuring, which obviously isn’t good (you’re counting the player’s own play in his teammates’ strength!).  The other method doesn’t include such data (Hockey Analysis’), but has the issue of small sample sizes, especially where players play together all year.  Regardless, it’s pretty clear that QOT matters a TON, and shouldn’t be ignored.

But the point of this article isn’t to say you should ignore zone starts and QOC.  You shouldn’t!  But please don’t look at such stats as justifications of good or bad numbers from a player – odds are, it simply doesn’t affect the player that much, really.

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