WHAT ARE SCORE EFFECTS
GLOSSARY
Score Situations:
Score Effects are the acknowledged differences in team performance based on the difference in score. There are popular methods are used for accounting for the score in whatever results are presented; we host two. The first, Score Close, was pioneered by Tore Purdy (aka JLikens) and simply includes situations where teams are within 1 goal of each other in Periods 1 and 2, and tied afterwards.
The second, manual score adjustment, has a few different predecessors:
Micah Blake McCurdy’s method, which is based on Poisson expectations;
Eric Tulsky’s, used to realign counts based on the time spent in each state;
Our own work with Poisson models, publicly dating back to 2012.
Not surprisingly, we went with our adjustments, and implement a full Poisson model for score, period and rink effects for each shot type by each danger zone. Adding the rink bias correction to our score and period correction was inspired by Schuckers and Macdonald.
PLAYING TO THE SCORE
When up a goal late in the game, the teams drastically cut back on offence. Similarly, the trailing team started putting more shots on net.
Interestingly, however, save percentage went up and so did shooting percentage, implying that the trailing team is taking more shots of lower quality, whereas the leading team is generating higher-than normal shot quality.
Whatever the explanation, this resulted in a huge percentage gap (almost 5%) in scoring rates, which made the leading team actually slightly more likely to outscore its opposition despite the one-sided shot differential.
We would need to look at a larger sample to see if the shot quality for the trailing teams is generally lower. I would suspect that it might be, but I am not sure. The evidence does appear to be there that the leading team will probably have higher than average shot quality for.
In Overtime:
In overtime, save percentage rose and shooting percentage went way down. It was interesting that these goalies’ teams were likely to get outscored in overtime. Even though all the teams had a good goalie in net they were just as likely to lose as to win once the game went into the fourth period. This suggests that overtime is quite random.
Outshooting Results:
Evidence suggests that your team is more likely to be trailing than leading if you get outshot over the first two periods of a game.
SCORING CHANCES BY GAME STATE
Shot ratio does vary according to the score, and the effect is fairly marked. As scoring chances are (highly) correlated with shots on goal, intuitively one might expect a parallel effect on scoring chance numbers.
1. He wasn’t convinced that sitting on the lead was a good strategy. I’m inclined to agree with him.
2. There isn’t much evidence that scoring chance quality varies by game state.
3. It’s difficult to say whether or not the effect is more pronounced later in the game.
WHEN DO SCORE EFFECTS TAKE PLACE
Score effects have a strong time-dependence.
Score effects play virtually no role outside of the third period.
Trailing teams outshoot their opponents, while leading teams get outshot. The effect becomes more extreme the closer we get to the end of the game and as the lead gets larger.
For most of the game, there isn’t much of a connection between the score and a team’s shooting percentage. It’s only late in the game that trailing teams start allowing a lot more scoring chances per shot while not producing high-quality chances at the other end of the ice themselves.
WHY DO SCORE EFFECTS EXIST
This occurs because teams have different incentives – if you are ahead then preventing the other team from scoring is more important than scoring yourself, so you’ll play less aggressively forcing the other team to work for it. Similarly, if you are behind then scoring becomes far more important so you are willing to take chances, pinch with your defensemen, have them jump into rushes and so on.
The NHL tiebreaking rules make hockey games non-zero-sum. If two teams tie, then the total number of points both get goes from 2 to 3.
The NHL rules actually make the incentive to score and prevent goals different when the score is tied, which we’ll cover in greater depth in future articles.
Score Tied: Early in the game, scoring and preventing goals are about equally important. When the score is tied you will gain or lose about a third of a league point on average if a goal is scored.
For The Team That Is Up: every minute of the game preventing a goal is more important than scoring.
For The Team That Is Down: Perhaps the most clear thing from this is the already obvious justification for pulling the goalie - the last couple minutes giving up a goal almost doesn't matter at all while scoring is worth close to a point and a half.
Scoring a goal right at the end of regulation is three times as beneficial for the team that is behind than it is costly for the team that is up.
The key time is 10-15 minutes out when the trailing team has a decent chance to get another goal and equalize.
With two minutes to go, scoring becomes 40 times as important as preventing the other team from putting the puck in your net if you are down 2.
IN-GAME EXPECTED POINTS
At the start of the game, the home team is expected to get 1.2 points, and the away team is expected to get 0.8 points.
In essence a team up a goal only has 0.5 EP to lose if they give up a goal, while the trailing team has 1.5 EP to gain by scoring the goal. This has obvious coaching and strategy consequences.
scoring a goal in the first is worth exactly the same value as preventing your opponent from scoring for the entire 3rd
SCORE EFFECTS ON ZONE ENTRIES AND SHOT DIFFERENTIAL
It seems clear that score effects are having a huge effect on neutral zone play, with the team that trails getting roughly a 4.8% boost compared to their tied results.
In other words, the much-discussed score effects on shot differential arise entirely from neutral zone concessions, with play in the attack zones having a neutral or mitigating effect.
However, winning the neutral zone isn’t just about getting the puck into the offensive end; the offense is much more effective if they can maintain possession of the puck as they enter the zone rather than dump-and-chase.
For forwards, the primary talent is retaining possession of the puck as they cross the blue line (and having linemates who do the same).
However, the correlation between the percent of OZ faceoffs won with the player on the ice and the team’s shots per OZ faceoff with the player on the ice is a modest 0.41.
UNDERSTANDING SCORE EFFECTS
What this means though, is that it’s imperfect to judge teams by “Shots For” and “Shots Against”. Those numbers are not absolute and have to be taken in context. A team that is better at shot differential with the score tied is going to score more goals in the long run. That is not really up for debate.
When you look at the end of the season, teams that generally out-shoot in tied situations have played enough minutes from behind that their shot overall totals recover.
Wins aren’t always predictive of the future, and neither are shot statistics, but if you’re attempting to forecast a team’s future, you could do a lot worse than by looking at a team’s shot differential while the score is tied or close.
SCORE EFFECTS & PENALTIES
We tend to see the leading team taking defensive zone penalties.
SCORE EFFECTS AND THE PLAYOFFS
(June 2014)
Score effects seem to be more prominent in playoff hockey than in regular season hockey.
By “playing it safe” coaches have effectively dumbed down the advantage they have when they put out their more skilled players. Instead of continuing to do what makes them great, they fall in line with the “playing it safe” mentality and no longer make skilled plays that separate themselves from the average to below average player.
Teams leading in the playoffs by two or more goals are not as good at driving play as they are in the regular season. When the stakes are higher, less” risks” are taken. I believe this is the driving force behind the amount of two goal leads that we see vanish in the playoffs.
One reason that we may see possession numbers lower in the playoffs vs the regular season is that teams in the playoffs are more likely than not to be better possession teams and have a stronger ability to control play when trailing. Teams that go into a defensive shell are even less likely to get the puck back for extended periods of time because of the oppositions proficiency at controlling the puck.
The current model is a breeding ground for comebacks and doesn’t seem to be “safe” at all.
PLAYOFFS AND SCORE EFFECTS
(April 2015)
By and large the trend is clear. Trailing teams get a boost going into important games.
The result indicates that there is a slight, but statistically significant association between the score of the series and the shot differential.
Loss aversion is having a clear impact, as teams trailing in the series have a sense of desperation that is not embodied by the leading squad.
while it’s a weaker effect, playoff series score effects appear to more closely resemble individual game score effects than one might have anticipated.
LEVERAGE
(Aug 2016)
When a team will likely gain a large number of points by scoring (for instance, when tied or trailing by one late in a game) we say that they are in a high offensive leverage situation.
Conversely, when a team will likely lose a large number of points by conceding a goal (for instance, when tied or leading by one late in a game) we say that they are in a high defensive leverage situation.
Defensive leverage is larger than offensive leverage almost all the time for both home and road teams.
This unfortunate discrepancy pushes teams to defend more than they attack in a way which is very reasonable: teams mostly have more to lose by conceding a goal than they have to gain by scoring.
coaches prefer to hide certain players from high-leverage situations instead of deliberately exposing certain players to high-leverage situtations, consistent with general risk aversion that we see in many coaching decisions.
Conclusion:
· Leverage is a measurable effect that varies non-trivially between games and in-games;
· Players who play more are more exposed to high-leverage situations;
· Even controlling for icetime, some players see varying levels of leverage; and
· This variation appears to be the deliberate choice of coaches.
WHAT DRIVES SCORE EFFECTS (SCORE SEQUENCING)
Leading teams sitting back drive score effects on shot rates more than trailing teams pushing.
Tied Game: There are many interesting features even just looking at tied scores; most obviously that the second period contains much more shooting than either of the other periods. Also striking is the slow decline in offence throughout the third period, and also the sharp drops for every single tied state coinciding with the second intermission.
One goal leads: Here the same pattern as in the tied scores is repeated: the second period contains more offence, and offence drops sharply as the third starts and continues to drop throughout the third.
One goal deficits: The second period continues to contain more offence, and the third period offence shows universal declines
For tied teams, a reduction in offence as the third wears on suits both teams – they will split three points if they can shepherd their game to to overtime,
Most Recent Goal Effects
it is nearly always beneficial to be the most-recent scorer, although the effect is a modest 5% or so.
Impact Of A Goal Scored:
this effect is also primarily driven by the scoring team, especially when the sharpest effect is the red line in the third period; where teams who score to tie the score late immediately start generating 10%-15% less threatening shot patterns despite the fact that another goal would be beneficial to them.
Impact Of A Goal Conceded:
In general, though, it seems that teams respond offensively to scoring (by generating less offence) and perhaps also defensively to being scored on (by allowing less); but mostly do not respond offensively to being scored on except near the end of games.
It appears as though score effects are driven primarily by leading teams and, while present throughout the game, have quite different characters in each period, and are most obvious in the third period
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