THE DEFENSIVE SHELL
HOW DOES THE DEFENSIVE SHELL WORK
as we get further into a game, Fenwick percentage drops significantly for the home team when they’ve got the lead in the 3rd period:
So here we see that there’s a very slight reduction in the away team’s shooting percentage when it’s trailing, and there’s a huge jump in the leading team’s shooting percentage.
Clearly a team has no reason to play in a defensive shell when they’ve got a man-advantage, and as the game progresses, a greater percentage of their shots come on the power-play, leading to higher shooting percentages.
THEORY BEHIND THE DEFENSIVE SHELL
The break even point for when to go into a defensive shell and when to continue playing normal hockey is at about 7-7.5 minutes for regulation win % and playoff win % systems and about 13 minutes for the point for an overtime loss system currently used during the regular season.
over a short period of time your are essentially dealing with small sample size issues and randomness becomes more important than long term skill. The reality is, over a short time one team is almost as likely to score as the other so which team scored next is close to random, if any team scores at all.
The most important thing when protecting a lead is simply reducing the likelihood that your opponent will score because the cost of your opponent scoring is far greater than the b enefit if you scoring (it is irrelevant whether you win 3-1 or 2-1, a win is a win in the standings).
the trailing team seems to have the edge which indicates teams probably go into a defensive shell too early on average, whether deliberately or otherwise.
THE DEFENSIVE SHELL DOESN’T WORK
Here’s the problem: the Defensive Shell doesn’t reduce the rate of opponent scoring. It actually INCREASES it.
It’s pretty well known that the defensive shell increases the rate of shots
Except, when trailing, teams’ shooting percentages actually increase
shooting % does NOT drop when a team is behind, despite them taking more shots.
teams score more frequently when BEHIND than when tied or up late:
THE DEFENSIVE SHELL MIGHT NOT BE THE PROBLEM
First of all, it’s important to note that score effects are the result of a combination of four very different forces (more on this in a future post).
1. Players naturally playing harder/more aggressively when trailing
2. Coaches coaching trailing players to push ahead and take risks
3. Players naturally being risk averse and not going their hardest when leading
4. Coaches coaching leading players to make the safe play (ie a contain or prevent defense)
the idea that getting hemmed in one’s zone leading late is simply a poor strategy that should be discarded – like the 1-3-1 forecheck or the overload power play – is misguided.
Shooting percentage when trailing is shown to be higher than that with the score tied right up until the end of regulation. But there’s a pretty logical reason for that as well. Teams tied near the end of regulation are playing for overtime. They are far more likely to dump shots from the blue line than to pinch to create opportunities. And both teams are far more worried about not allowing a goal against than scoring a goal for. There is massive loss aversion in play here; shooting percentage is bound to drop. You can’t compare the two situations because looming overtime (or more specifically the loser point) is a confounding variable.
So yes, scoring rates are higher against teams protecting leads than against teams late in tie games, but that doesn’t mean that the defensive shell, as a strategical maneuver, is responsible for that. Impending overtime, as well as natural factors that are difficult for coaches to account for, could just as easily be responsible.
PROTECTING A LEAD
· Holding leads is a repeatable skill that will stay consistent for a team, BUT
· protecting leads is almost entirely a function of a team’s Goals For % and does not add any additional information to whether a team will win or lose.
there is no “protecting a lead” skill
Good teams protect leads because they tend to score more than their opponents all the time. Bad teams tend to blow leads because they always tend to get scored on.
If a team is blowing a lot of their leads, the solution isn’t necessarily to get more shutdown players who can prevent the next goal; rather it might be to get better offensive players so that the lead becomes larger.
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