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Introduction to Hockey Analytics Part 5.1: Evaluating Neutral Zone Play: Zone Entries

The Professional Hockey rink is divided into three "zones" - the offensive zone, the defensive zone, and the neutral zone. As you'd think, a player's play in each of these zones is important - and thus any attempt to determine how valuable - or simply how good - a player is needs to deal with the player's capabilities in all three of these zones.

In order to measure a player's capabilities in the offensive zone, we have things like Shots on Goal per game, Goals, Assists (mostly), Shots directed toward the net, etc. In order to measure a player's capabilities in the defensive zone, we have things like goals allowed while a player is on the ice, blocked shots, save % (Goalies are only in the defensive zone), etc.

But we don't really have statistics to measure the value of a player's contribution in the neutral zone. Instead, what hockey fans have been forced to use for these efforts are stats that attempt to measure a player's total play on a whole. Stats like +/-, corsi, & fenwick attempt to measure a player's overall play, which obviously should include a player's neutral zone play. But none of these stats can really tell us who is good and who is bad at neutral zone play.

This is a problem. In fact, it's a major problem. Because Neutral Zone play is EXTREMELY important.

Over the past season, Eric T* over at NHLNumbers and BroadStreetHockey and Geoffrey Detweiler (also of Broad Street Hockey) have attempted to determine the value of neutral zone play in hockey. How? By going over every Flyers game and charting every single time at even strength each team took the puck from the neutral zone and got it into the offensive zone. In addition to noting how often each team got the puck into the offensize zone, Eric and Geoff looked at HOW teams did so - whether they carried the puck in, passed it in to a player crossing the blue line, dumped it in, or tipped the puck into a corner (essentially the same as a dump). They referred to this as tracking ZONE ENTRIES.

*This is the second time (at least) I've mentioned Eric T's work in this series and it's for a good reason: his work is really really good. If this series interests you, you should be checking nhlnumbers.com quite regularly where Eric posts his findings every now and then - his work is fascinating and often groundbreaking and he writes in a style that is very easy to understand. And the other guys at NHLNumbers are great as well.

What Eric found was fascinating: the amount of shots that resulted from each zone entry was on average dependent not upon what players were on the ice for the zone entry but rather whether the zone entry was made with control (by carrying in the puck or passing it to a player cutting into the zone) or without control (by a dump or tip in). In other words, it didn't matter much if it was Sean Couturier or [insert flyers 4th liner here] entering the zone - what mattered was HOW the puck was brought in:*

Carry-in Pass-in Dump-in Tip-in
Shots per entry 0.57 0.56 0.25 0.26
Goals per entry 0.039 0.035 0.014 0.017

Table 1: Eric T's discoveries as to the Shots Per Entry and Goals Per Entry for the Philadelphia Flyers based upon how the puck was brought into the offensive zone. As you can see,an entry with possession - via carrying or passing in the puck - results in basically twice as many shots (and goals) for the attacking team as an entry without possession (via dump or deflection in).


This is not to say that good players don't do more with the puck in the offensive zone; rather good players do more on offense because of HOW they get the puck into the offensive zone. John Tavares gets more shots on net per zone entry than Marty Reasoner not because he's a better offensive player, but because Reasoner dumped the puck in a lot (%) while Tavares most of the time entered the zone with possession (generally by carrying the puck in himself).

But: several of the things we previously attributed to offensive and defensive play - shots on goal, shots, even goals to a certain extent - are driven in large part not by offensive or defensive play, but by NEUTRAL ZONE play. And yet none of the standard NHL tracked statistics really quantifies neutral zone play!*

*This is not to devalue the importance of offensive/defensive zone play entirely in driving these stats - neutral zone play doesn't matter going into offensive/defensive zone faceoffs of course, which are not infrequent in a hockey game. So Zone-Start% still matters.

Now Eric's results are of course preliminary to an extent - his work dealt only with him tracking the Flyers. Since his presentation, data on the Minnesota Wild has confirmed his findings and several other individuals (myself included) have started tracking the neutral zone play of their teams last year (I've started working on the Isles).

The implications of this finding are fascinating and bear examination. Here are a few examples:
1a. A player who gets a lot of shots on goal over a season despite not being on a line that enters the zone with possession is likely due for regression and his shot totals/goals/possession #s are likely going to decline.
1b. The opposite is also true: A player who carries the puck in frequently but isn't getting many shots on net is likely getting unlucky and is likely to pick up his play in the future. He's going to regress but in a good way.

2. Teams may be playing less efficiently than they might be otherwise because their strategies are resulting in them playing too conservative - they're too eager to dump in the puck because it's easier when being more aggressive will result in better zone entries and more shots on goal, even if it results in fewer zone entries.
----In this regard, it may be more worth it for teams to regroup if they find they can't force their way into the opponent's zone and to try again rather than to dump the puck and hope to win a chase/deflection war.

3. Teams may be able to produce more efficient lines by ensuring that each line has at least one guy able to play well in the neutral zone and to carry the puck over with possession --> for example, the Tavares line works well with Matt Moulson not because Moulson needs Tavares to score but rather because Tavares gets the puck into the opponents' zones efficiently allowing for Moulson, a not-great neutral zone player, to score more frequently. If Moulson was instead on a line with no good neutral zone player, he would be unable to have any opportunities for success (this may have been the case with Nino Niederreiter last year).

And I'm only scratching the surface here. Suffice to say, the implications are huge.

This is not to say neutral zone play is everything of course - you still need goal scorers (such as say Matt Moulson) once you're in the offensive zone, and offensive/defensive zone play is of course still important - heck in possessions that arise out of faceoffs in the offensive/defensive zone, there's no neutral zone play involved! Thus players can of course be valuable players without being neutral zone aces if they're used properly - to use Matt Moulson as an example again, Moulson's goal scoring offensive zone prowess is best utilized by getting Moulson extra faceoffs in the offensive zone (Done by the Isles), power play time (Done by the Isles), and by pairing him with two players who can carry the puck into the zone (Done by the Isles in Parenteau and Tavares) to give him time to set up.

That said, neutral zone play is a huge factor in the game which now needs to be taken account of.

CONCLUSION:

The main point here is that neutral zone play seems to be incredibly important toward winning hockey games, and yet prior to Eric's work we had no way really of measuring the value of neutral zone play.

The Zone Entry Project is the first attempt we've made to change that, and it promises to answer some interesting questions about the value of hockey players. I hope to give you guys some sample results soon and hope that you guys will keep an eye out for developments on this front.

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The Intro to Hockey Analytics/Advanced-Hockey-Statistics Primer so far:

Part 1: - What is the field of Hockey Analytics and Why Might You be Interested?
Part 2.1: - The Importance of Context Part 1 - Time on Ice
Part 2.2: - The Importance of Context Part 2 - Evaluating the Difficulty of Certain TOI through QUALCOMP and Zone-Starts
Part 2.3: - The Importance of Context Part 3 - Evaluating (and Compensating for) the Effect of Teammates via QUALTEAM and Relative Measures
Part 2.4: - The Importance of Context Part 4: The Concept of the Replacement Level Player
Part 3 - The Perils of Sample Size
Part 4.1 - Introduction to Hockey Analytics Part 4.1: Possession Metrics (Corsi/Fenwick)
Part 4.2 - Introduction to Hockey Analytics Part 4.2 - Possession Metrics: The Various Forms of Corsi Available on Hockey Sites
Part 4.3 - Introduction to Hockey Analytics Part 4.3: Possession Metrics: Fenwick a Measure of Effective Possession
Part 4.4 - http://www.lighthousehockey.com/2012/12/8/3743932/introduction-to-hockey-analytics-part-4-4-possession-metrics-scoring

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