GUEST COLUMNIST: Another look at team defence and goaltending throughout the league

Frjohnk (“Father John” or “Padre” as we’ve taken to calling him) @ Lowetide has been doing some terrific work to refine our understanding of goaltending and defenses through the league, using the war-on-ice scoring chance data.  As he doesn’t yet have a blog and therefore casts these pearls within LT threads (making them somewhat harder to find and reference), I’ve suggested to him that I can make them available as a “guest post” here at NerdAlert.  He’s cool with the idea, so here you have it: the first ever NerdAlert Guest Columnist, Frjohnk!


About a month ago, I looked at what each team gives up in regards to shots and where these shots are from. http://lowetide.ca/2015/03/15/five-things-that-could-improve-the-oilers-next-season/

I have been looking for the holy grail stat that measures team defence. I believe the holy grail of the team defence stat will be found when we can measure the quality and the quantity of shots allowed. While we can measure quantity of shots, we cannot get a true measure for quality of shots, yet. But war on ice has a stat that lets us know the location of where the shots come from which are labeled high, medium and low danger locations. These 3 different areas produce different shooting percentages, so I can give each shot location a weighting based on shooting percentage and match it with what each team gives up in regard to shots from these locations and come up with a stat called “team defence.”

Last time, I calculated the team defence stat by using all situations (PP, PK, even strength, goalie pulled). This time, I only used 5 on 5 with the score adjusted as PP, PK and blowout time might have an affect on how the numbers come out and I will do this same calculation with all situations and compare.

So to warm up, let`s look at save % in the 3 areas of low (perimeter) medium (beside the slot) and high (slot) danger locations of the 30th place team, 1st place team, league average and where EDM sits.

5 on 5 score adjusted
Overall save%
EDM………..0.901…(30th)
Leag Avg…..0.922
MTL…………0.936…(1st)

Low Danger Save%
EDM…………0.957..(30th)
Leag Avg…..0.973
PHI…………..0.986..(1st)

Med Danger Save%
EDM………….0.900……(30th)
Leag Avg……0.925
BOS…………..0.946..(1st)

High Danger Save%
CAR….………..0.797…(30th)
EDM..………..0.824…(21st)
Leag Avg…….0.834
NJD……………0.862…(1st)

Now here is a snippet of how the best and worst teams, the league average and Edm for what they give up from the different shot locations.

Low Danger Location Shots Allowed/60min
Buffalo………16.36 (30th)
Tampa……….11.04 (1st)
Edm………….12.49 (8th)
League Avg…13.19

Medium Danger Location Shots Allowed/60min
Buffalo……..9.78 ( 30th)
Wash……….6.80 (1st)
Edm…………8.24 (23rd)
League Av…7.77

High Danger Location Shots Allowed/60
Buffalo…….9.95 (30th)
Nashville….6.44 (1st)
Edm………..8.80 (26th)
League Av..7.90

So I had the numbers for all the teams and what they allowed from each shot location.
I also know that the shooting % from the high danger area is 16.4%, from the medium danger area its 7.5% and from the low danger area its 2.7%.

I will use ANA as a snippet of the work I did.

For ANA = Low danger location shots allowed 13.56, medium danger location shots allowed 7.16, high danger location shots allowed 7.07. This equals 27.79 shots allowed per 60 min. Now if we plug in the league average shooting %`s for each location, the cumulative weight of each shot allowed against Anaheim would suggest the opposing team scoring 2.08 goals per 60 min. From there, we take total shots (27.79) and expected saves (25.71) (total shots – expected goals) and do the calculation to get an expected save % of .925

Expected Save%……Actual Save %……Difference
ANA….0.925……………..0.919……………….-0.006
ARI……0.921……………..0.915……………….-0.006
BOS….0.924……………..0.929………………..0.005
BUF…..0.922…………….0.921………………..-0.001
CAR….0.919……………..0.909……………….-0.010
CBJ…..0.923……………..0.918……………….-0.005
CGY….0.919……………..0.922………………..0.003
CHI……0.920…………….0.935…………………0.015
COL…..0.921…………….0.926…………………0.005
DAL…..0.921……………..0.912……………….-0.009
DET…..0.924……………..0.926………………..0.002
EDM….0.918……………..0.902……………….-0.016
FLA…..0.928……………..0.923……………….-0.005
L.A……0.923……………..0.926…………………0.003
MIN…..0.926……………..0.918……………….-0.008
MTL….0.924……………..0.936…………………0.012
N.J……0.922……………..0.935………………..0.013
NSH….0.928…………….0.931…………………0.003
NYI……0.916…………….0.914………………..-0.002
NYR…..0.925…………….0.931………………..0.006
OTT…..0.926…………….0.930…………………0.003
PHI…….0.923…………….0.930………………..0.007
PIT…….0.919…………….0.925………………..0.006
S.J…….0.921…………….0.920……………….-0.002
STL……0.922…………….0.923………………..0.001
T.B…….0.918…………….0.919………………..0.001
TOR…..0.918…………….0.918………………..0.000
VAN…..0.920…………….0.917……………….-0.003
WPG….0.922…………….0.928………………..0.006
WSH….0.923…………….0.924………………..0.001
League average 5 on 5 score adjusted save percentage was .923.

So how to read this: When the difference = 0.000 like Toronto, you got exactly league average goaltending. When the difference is a minus like Florida, that team got below league average goaltending. When the difference is positive like Colorado, that team got above league average goaltending.

The lower the expected save %, the harder the job that the goalie had. Anybody surprised that EDM and TOR goalies had one of the toughest jobs? Or with higher expected save percentages, the Rangers and Nashville goalies had the easiest jobs? Take a look at the defence of those teams, should not be much of surprise.

“Expected save percentage“ does not tell us the quantity of shots and so we are not sure what exactly teams are allowing on net. So to get a clearer picture of team defence, we need to incorporate “expected save percentage“ and totals shots per 60 min. Here is where we get “expected goals against per 60 min“ which I am going to call `team defence“.

Expected goals against /60…Actual goals against/60…Difference
ANA…….2.08………………………..2.20…………………….-0.12
ARI……..2.46………………………..2.60……………………..-0.14
BOS…….2.19………………………..2.00……………………..0.19
BUF…….2.83………………………..2.70……………………..0.13
CAR…….2.16………………………..2.40…………………….-0.24
CBJ…….2.44………………………..2.60…………………….-0.16
CGY……2.38………………………..2.30……………………..0.08
CHI……..2.39………………………..1.90……………………..0.49
COL…….2.53………………………..2.40……………………..0.13
DAL…….2.18………………………..2.60…………………….-0.42
DET…….2.04………………………..2.00……………………..0.04
EDM……2.42………………………..2.90…………………….-0.48
FLA……..2.02……………………….2.20……………………..-0.18
L.A………1.98………………………..1.90……………………..0.08
MIN……..2.01………………………..2.20…………………….-0.19
MTL…….2.22………………………..1.90……………………..0.32
N.J………2.24………………………..1.90……………………..0.34
NSH…….1.98………………………..1.90……………………..0.08
NYI……..2.31…………………………2.40…………………….-0.09
NYR…….2.23………………………..2.00……………………..0.23
OTT…….2.33…………………………2.20……………………..0.13
PHI……..2.25…………………………2.10……………………..0.15
PIT……..2.20…………………………2.00……………………..0.20
S.J………2.27…………………………2.30……………………-0.03
STL…….2.06………………………….2.00…………………….0.06
T.B……..2.15………………………….2.10…………………….0.05
TOR…….2.68…………………………2.70…………………….-0.02
VAN…….2.31…………………………2.40…………………….-0.09
WPG…..2.08…………………………1.90……………………..0.18
WSH…..2.09………………………….2.10…………………….-0.01

Expected goals against league average is 2.25 goals per 60 min while using 5 on 5 score adjusted.

So what does the difference mean? If there is a minus on the difference, it means the goaltending for that team allowed more goals than what the league average did factoring where shots came from. If it`s a positive, then goaltending for that team was above league average.

If a team has an expected goals against average less than 2.25 goals per 60 min, the team defence is better than league average, if expected goals against average is more than 2.25 goals per 60 min, the team defence is worse than league average.

Its not perfect, as it does not measure breakaways, rush shots, or one timers directly, which some teams allow more than others (I`m looking at my beloved Oilers right here) and of course make goaltenders jobs even tougher.  As Gmoney points out and reminds me, break aways, and rush shots are labeled in the “high danger location”, so they are measured. But I’d like to see the stats that would measure breakaways, rush shots and one timers as it would give us an idea on how easy or tough a goalies job is every night. For most Oiler fans who see the Oilers team defence ranked at 25th, this little exercise may pass the smell test. For others, it might not. And thats OK too.

Up next, I will be looking at some goalie targets and plugging in their stats along with what Edmonton gave up for shots. A heads up, preliminary work shows most of these goalie targets see a hit to their save percentage numbers. Should we be surprised?

Advertisements

4 thoughts on “GUEST COLUMNIST: Another look at team defence and goaltending throughout the league

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s