DEFENSEMEN’S ABILITY TO INFLUENCE ON-ICE SV%
(May 2010)
The ability of defensemen to affect shot quality against does exist in the population, but it is so small that we will never be able to sensibly apply it to any player in particular.
Scoring chance % may not be everything for defenders, but it’s almost everything. And it repeats really well just as a raw number
INVESTIGATION INTO SV%
PDO is not a random variable that automatically regresses to 1000, in fact many teams had more or less than their share of expected above or below average seasons, based on probability theory.
it immediately becomes clear that certain teams have received consistently high save percentages, while others have received consistently low team save percentages.
a team’s save percentage tendency is not necessarily towards league average.
The conclusion is clear: team save percentages do not regress to league average, even over the long term.
Considering that save percentage is one of the components of PDO, I’d suggest that as a community we start to question the assumption that PDO necessarily regresses to 1000.
SV% REGRESSION
(93.5% = good, 88.5% = bad)
Forwards:
Their on-ice save percentage over the first three years was essentially useless as a predictor of how they’d do in the next three years
Over a three-year span, it doesn’t matter whether a forward sees his team stop 94% or 90% of the shots with him on the ice at 5-on-5; either way, the best guess for how he’ll do in the next three years is league average.
Defensemen
While there may be a sliver of repeatable talent for defensemen preventing the opponents from getting high-percentage shots, after three years of data we aren’t even close to being able to reliably tell who’s good at it.
DEFENSEMEN HAVE NO CONTROL OVER SV%
Ultimately, defenders fail in being able to sustainably improve or worsen their goaltender’s save percentage.
There are three consequences to this discovery.
· One, as already discussed, that defensemen’s control of save percentage is minimal enough that adding on-ice save percentage effects do not add value in player evaluations other than looking at those likely to regress to the mean.
· Two, that a defender’s impact on shot metrics (specifically looking at both Corsi% and relCorsi%) is (currently) still the best way to approximate a player’s value in outscoring.
· Three, that for the most part a goaltender owns their save percentage (once sample is large enough).
BOOSTING SV%
we know players can impact save percentage because score effects are real.
Furthermore, in recent months the following have been discovered:
· Shots taken on the rush are more difficult shots resulting in higher shooting percentages.
· Based on the zone entry/exit work by Corey Sznajder we have seen that players and teams allow successful zone entries against (which essentially result in more rush shot opportunities) at different rates.
These two observations taken together implies that the players that are better at minimizing clean zone entries against effectively should be able to boost their goalies on-ice save percentage.
POSSESSION ISN’T EVERYTHING EXCEPT FOR DEFENSEMEN
Forwards Can Control SH% (To An Extent)
forwards who have above or below average Sh%s in their first four seasons (08-11) still tend to remain above or below average over their next three seasons (12-14). This indicates that there is more to a forward’s on-ice shooting percentage, over extended periods, than just random variance.
Defensemen Have No Control Over SH%
defensemen have a minimal impact on their on-ice shooting percentage.
Forwards On Ice SV%
Forwards can’t control on-ice save percentage like they can shooting percentage.
Defensemen On Ice SV%
The results don’t seem to differ much from the forward data.
The fact that a defenseman’s PDO is practically beyond their control implies that their ability to drive/anchor possession (CF/FF/xG) stands as an optimal tool for evaluation (at even strength) on its own.
WHY ON-ICE STATS MAY NOT BE COMPLETELY USELESS
The current consensus is that there has been no evidence found to date to show that impacting on-ice Sv% is a repeatable skill. Instead, when you look across the league as a whole, what you find are outcomes that essentially resemble randomness.
on a league-wide basis, neither forwards nor defensemen are able to consistently display above/below average performance on the metric.
As a result, I wanted to investigate how Sv%RelTM’s predictive capabilities changed when a skater is consistently playing with the same starting goalie.
Save % Relative to Team – Defensemen only
There appears to be almost no relationship (R2 < 1%) between time periods in terms of a defenseman’s ability to impact his team’s on-ice Sv%.
Save % Relative to Team – Defensemen & Forwards
There actually was some relationship – something otherwise unheard of in this type of analysis.
Save % Relative to Team – Forwards only
By removing defensemen altogether (getting to a total n=25), you can see that the predictive value of Sv%RelTM reaches the highest found in any analysis I have reviewed – an R2 of 41%
The relationship shown here for forwards indicates to me that it is in fact a skill, whether or not it would be displayed to the same degree on a different team or with a different goalie.
Much like CF% has significant team-level and player-level components – and won’t necessarily be directly transferrable between teams and systems – we still think of players as being strong/weak at driving shot-attempt differentials. I think the same logic can be applied here.
DOES PAST SV% PREDICT FUTURE SV%
I decided to check whether future results for any of the 3 on-ice save percentage variables (Sv%, Sv% Rel, and Sv% RelTM) could be predicted using past results of any of the 3 on-ice save percentage variable
Even in the best case we’re only explaining less than 10% of the variability in our metrics using a player’s past results and any contextual changes that occur.
The implication of this is that we need to be extremely careful when we use save percentage related statistics to describe the defensive play of skaters. We simply can’t say with a high degree of confidence that the players who have posted the best on-ice save percentage (or SvPct RelTM or SvPct Rel) in the past will be the players who post the best on-ice save percentage (or SvPctRelTM or SvPct Rel) in the future.
Even if we can know exactly what situation we’re going to put a player into, predicting how their save percentage is going to come out is a rather futile exercise – their past save percentage just doesn’t give much information to go off of.
DEFENSEMEN IMPACT ON TEAM SV%
(Sept 15, 2016)
Basically, it's all random. Forwards or defense. Can't predict OISV% and it always regresses to the mean.
individual defencemen don’t appear to have an impact on their team’s save percentage.
A player’s on-ice or team-relative save percentage varies greatly from year to year. Because there’s such volatility and unpredictability, it’s impossible to draw a connection between a player’s given on-ice or team-relative save percentage and a genuine talent.
there is simply zero evidence that a player can truly impact his team’s save percentage over long periods of time.
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