Skill, Coaching, or Randomness: What Goes Into Open-Play Performance in the Offensive, Defensive, and Neutral Zones Josh Smolow

Where Hockey Is Played Hockey is played in Three Zones: The Offensive Zone, the Neutral Zone, and the Defensive Zone. Conventional Hockey discussion, particularly commentary during games, often attributes particular results to good play in one or more of these three zones. However, Conventional Hockey statistics provide no way to really judge performance of a team in any of these three zones, to evaluate any of these statements.

Neutral Zone Tracking Back during the season, Geoffrey Detweiler and Eric Tulsky of Broad Street Hockey decided to try and fix that by tracking play in the Neutral Zone. Their Method: In every Flyers Game that season, Geoff would record each time each team moved the puck out of the neutral zone and into the opponents’ zone. (Zone Entries) For each Zone Entry, Geoff would record the time, player making the entry, and most importantly, the TYPE of entry: Was it a controlled entry (entering by Carry-in or Pass-in) or an uncontrolled entry (entering by Dump or Tip-In) Carrying-InDumping the Puck In

Neutral Zone Tracking When a Season’s worth of Data was collected, Eric Tulsky analyzed the data and found several interesting results. In particular he found that entering the zone with control resulted in over TWICE as many unblocked shot attempts as uncontrolled entries (Dump- Ins). In Addition, he noticed that failed attempts at carrying-in weren’t as detrimental as previously thought, suggesting teams are resorting to dumping in too often. Using the average fenwick values for each type of Entry, Eric created a statistic he called “Neutral Zone Score” which could measure on-ice neutral zone results for players.

Offensive and Defensive Zone Scores Credit: Eric Tulsky, NHLNumbers.com In addition, using the average # of shot attempts per entry, Eric was able to conceive of Offensive and Defensive Zone Score statistics as well, as broken down below: The Offensive and Defensive Zone Score statistics essentially measures the estimated Fenwick of a team based upon its offensive/defensive zone play alone, as if the team was perfectly even with the opponent in the other two zones. Note: These metrics only deal with zone play from open-play and don’t deal with play after faceoffs in either the offensive or defensive zones.

Is Performance in all Three Zones Repeatable? Credit: Eric Tulsky, NHLNumbers.com Eric’s initial analysis using these three zone score metrics found a fascinating finding: Individual performance in the offensive and defensive zones wasn’t repeatable – only NEUTRAL zone performance was. This suggested that differences in corsi/fenwick numbers were driven near entirely by performance in the NEUTRAL zone, rather than from play in the other two zones. However, Eric noted that these results came from only examining the Flyers. Later Minnesota Wild data from the same season WOULD show defensive zone repeatability, although the #s didn’t seem too credible.

Shutdown Line Project A few people decided to start tracking other teams in the seasons following Eric’s analysis. One such tracker, Corey Sznajder decided to do what seemed impossible: To Track EVERY game in the NHL for every team during the season. Remarkably, Corey finished about 60 games for each team (a full season for 5 teams) before the season started and he was hired to work for a team. This provides us with a database of neutral zone results for every team during the season. We can now actually test whether Eric’s results persist throughout the league, or whether he simply found a Flyers related quirk. An additional benefit of this is that by having every teams’ data tracked by the same individual, we nearly eliminate the problem of Tracker Bias.

Split Half Reliability To test repeatability of each team’s performance in all three zones, we are going to test for Split-Half Reliability What this means is that we are splitting each team’s sample in two, with one sample consisting of odd-games and one consisting of even games. A comparison of these two gives us an answer of whether a result in a metric is real – the result of skill somewhere – or if the result is simply the result of variance.

Team Split Half Findings On a Team Level, it’s clear that performance in all three zones is reliable – a team that is excellent in the offensive, defensive, or neutral zone in odd games is likely to be excellent in even games. (Neutral Zone Performance has the strongest reliability, but all three zones’ #s are pretty strong) This suggests that teams can be successful through being strong in any of the three zones – not just one in particular. (ex. Devils, Sharks)

Individual Split Half Findings In order to test individual Neutral, Offensive, and Defensive zone Repeatibility, we need to separate the individual performance from the team. Hence we’re now using “Relative” versions of these statistics. The results of the split-half analysis are below: The Results show basically no offensive or defensive zone score repeatability for individuals, similar to what Eric found in his initial results. By Contrast, Neutral Zone Score does appear reliable for individuals, although the correlation is not high. This strongly suggests players have individual control over the neutral zone.

Team by Team Individual Split Halves Given that we found teams seem to have control over open-play offensive zone and defensive zone performance, we should look again at individuals, and see how repeatable their performance in the three zones is just among their own team. The Correlations for each team’s individuals’ are to the right. Only Five teams show offensive zone repeatability, while only Six show defensive zone repeatability, suggesting our overall league results aren’t different from results within a system. That said, the Isles’ and Kings both showed repeatable performance in the offensive zones, which dovetails with prior research done by different trackers for those teams in different years, suggesting there may be something more here.

Thoughts on Results: Who’s driving These Numbers? It’s clear that there is a team skill in posting better or worse numbers in the offensive and defensive zones during open play. Some teams are able to thrive (or fail) based upon a consistent failure in the offensive and defensive zones. Yet Individuals don’t seem to show that same repeatable skill. This suggests team systems and execution of such matter more significantly than individual players at times. Adding an individual player to improve the offensive or defensive zone shot numbers of a team may be a strategy more often than not destined to fail unless such a player is a good neutral zone player. Excellent Two-Way Neutral Zone Players should obviously be highly valued. That said, team effects are strong here as well.

Additional Thoughts: Where do we need to go from here? Year over Year Repeatability: The above analysis dealt with split halves within the same season, but a further analysis would hopefully deal with zone scores for individuals and teams for year to year. Looking at individual elements of each zone score: The Neutral Zone Score basically comprises of 3 elements: % of entries made by each team, % of entries made with control, % of entries opponents make with control. Similarly, Ozone and Dzone performance deals with two elements: shots off of controlled entries and shots off of uncontrolled entries. And each of these elements can sort of be broken down further – a look at how well teams and individuals are able to recover the puck after dumps, would be a subpart of OZ and DZ scores. Are any of these elements more repeatable or more important than others? Looking at Coaches, Players, and Teams when they shift around: How does a coaching change affect teams? Players?

Credits Massive Thanks and Appreciations are needed for: Eric Tulsky Muneeb Alam Corey Sznajder Without these individuals, this work wouldn’t have been possible.