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The evolution of hockey statistics – an ongoing story
Bruce McCurdyAnalytics, Big Data, and the Cloud2012 April 25
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Traditional game summaries
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1967-68 Plus/minus formally introduced, as well as individual shots on goal / Shooting %
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1983-84 Goaltender save percentage added
Grant Fuhr
Grant Fuhr
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1998-99 Time on ice published, opening the door for rate stats
Chris Pronger
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1998: NHL introduces Zone Time
… but turfs it in 2002. Why?!
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1998: NHL starts to (sporadically) maintain Real Time Scoring System (RTSS)
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…but there remain huge problems due to lack of standardization & rink bias
Oilers have twice as many giveaways as Florida … or do they?
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• Ranking of teams’ RTSS home and away yields results that might as well be randomized for giveaways and takeaways, and very nearly so for hits and blocked shots.
• Whereas the same exercise for Goals For yields a crudely similar ordering home to away.
• Significant home scorer bias in turnover stats. 45% more giveaways and 33% more takeaways by home teams league-wide!
• As a result RTSS is highly unreliable, serving to rank players within a given team but almost useless for comparing players from different clubs.
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2002-03: NHL introduces play-by-play reports
… though problems remain with accuracy of some data, e.g. shot distance
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“Stripping” of PxP data allows detailed on-ice analysis of individual playersEven-strength shots / Fenwick / Corsi from timeonice.com
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Head-to-head match-ups (timeonice.com)
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Customizable, sortable stats from behindthenet.ca
Available stats: Even strength / powerplay / shorthandedScoring per 60 minutesOn/off ice plus/minus per 60On/off ice shots / Fenwick / Corsi per 60On-ice Sh% / Sv% / PDOQualComp / QualTeamPenalties drawn / takenZoneStart / ZoneFinish
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• Many stats need to be parsed in terms of positive / negative /neutral game states, e.g.:
• Leading / trailing / tied (score effects are HUGELY important)
• PP / PK / EV • O-zone / D-zone / neutral zone
• Taken in isolation without context, modern stats will be distorted; e.g. “soft minutes” players used in offensive situations should be expected to have positive numbers in things like Relative Corsi
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"A chance is counted any time a team directs a shot cleanly on-net from within home-plate. Shots on goal and misses are counted, but blocked shots are not (unless the
player who blocks the shot is “acting like a goaltender”). Generally
speaking, we are more generous with the boundaries of home-plate if there is dangerous puck movement immediately preceding the scoring chance, or if the scoring chance is
screened. If you want to get a visual handle on home-plate,
check this image."
Scoring chances
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One weakness to the current method is that “home plate” isn’t best template for scoring area
Another is that scoring chances are just 1’s and 0’s – no extra weight for first class chances as suggested by heat map colour coding
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Actually, scoring areas …which vary for different types of shots and manpower situations.
Scoring chance model is greatly simplified from this reality.
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Common SC errors and outcomes• NHL data doesn’t properly record on-ice players• +1 or -1 for selected players• Scoring chance improperly credited (or missed)• +1 or -1 for 10 players• Scoring chance recorded at wrong game time• +1 or -1 for up to 20 players• Scoring chance recorded but for wrong team• +2 or -2 for 10 players
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Neilson Numbers
• Based on ideas of Roger Neilson• Assignment of individual responsibility on scoring chances for
and against• Requires an extra degree of qualitative judgement over and
above deciding whether a scoring chance has occurred• Eliminates false positives/negatives, however individual numbers
don’t reconcile to team totals• Fewer recording errors than on-ice scoring chances as players are
identified as part of the process• Same system can be used to assign unofficial assists on GF or
errors on GA• Reliant on a knowledgeable scorer, but as with other scoring
chance systems, would work better if 3 or 5 scorers worked independently, then pooled results.
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Sample box:
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Zone Start:fad or trend?
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Possession
• “Hockey is a transition game: offense to defense, defense to offense, one team to another. Hundreds of tiny fragments of action, some leading somewhere, most going nowhere. Only one thing is clear. A fragmented game must be played in fragments. Grand designs do not work. … Before offense turns to defense, or defense to offense, there is a moment of disequilibrium when a defense is vulnerable, when a game’s sudden, unexpected swings can be turned to advantage. It is what you do at this moment, when possession changes, that makes the difference.”
• – Ken Dryden, The Game
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• “It is noteworthy that in general … our teamwork was considerably above our main contenders. In the game against the Canadian team, the players of the USSR squad made 110 passes, while the Canadians made 60 passes; in the game against Czechoslovakia we made 106 passes, they made 70; in the game against Sweden we made 49 more passes than they did. … This is an indication of quite stable habits and a high culture of playing, a correct understanding of the game by the Soviet players.”
• -- Anatoli Tarasov, Road to Olympus
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Good pass: plus. Bad pass: minus.
Good clearance: plus. Bad clearance: minus.
Good rush: plus. Bad rush: minus.
Good shoot in: plus. Bad shoot in: minus.
Tarasov Numbers
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…and many more advanced ideas
• Goals Versus Threshold (GVT)• Defence Independent Goalie Rating (DIGR)• Shot Quality (SQF / SQA)• Preditcted Goals Scored (PGS)• Zone Start Adjusted Corsi (ZSAC)• Etc. …• No time to do them all justice here• Thanks for listening!