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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 players
Even-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 / shorthanded
Scoring per 60 minutes
On/off ice plus/minus per 60
On/off ice shots / Fenwick / Corsi per 60
On-ice Sh% / Sv% / PDO
QualComp / QualTeam
Penalties drawn / taken
ZoneStart / 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 isnt best template for scoring area
Another is that scoring chances are just 1s and 0s 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 doesnt 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 dont 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 games 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!
