The game of hockey is all about chance, especially in the NHL, any team could win on any given night. Because of this teams are looking for any advantage they can get over their opponent to tip the odds in their favor.
Often we hear about team scoring when their opponent has been on the ice for an extended period of time, but does this significantly help a team? Looking into individual shot data we can answer this question.
All data in this post looks at 5 vs. 5 situations (no power plays or empty net) in the NHL over the last three seasons. While there are multiple ways to measure time on ice (TOI) I chose to just look at the average, rather than the max, or separating out defensive players from offensive.
The first graphic shows attacking team’s average expected goal value (xGoal) based on the defensive team’s average time on ice. A 10 period moving average line has been added as well – this is a moving average of the previous 5 and the next 5 seconds.
xGoal increases pretty steadily from about 0 seconds to 25 seconds, it then starts to flatten off. At about the 80 second mark, xGoal values start to spread out and become volatile.
The peak occurs at about the 130 mark, but it’s hard to say if this should be really considered the ideal time to try and keep defensemen on the ice. Though, it appears that xGoal increases as a team keeps its opponent on the ice.
The second graphic is similar to the first, but rather than looking at defensemen TOI, it looks at the offensive team’s TOI.
This graphic is similar to the first in that xGoal slowly increases and then begins to scatter around the 80 second mark. The difference though is the moving average line really only increases (aside from a slight dip between 90 and 100 seconds).
This makes sense when you think about it. If an offensive team is on the ice for an average of 80 – 100 seconds this suggests a good offensive run with sustained pressure in their opponent’s zone. Goals tend to come from pressure like this.
The final graphic looks at xGoal and how it relates to the difference between the defense’s TOI and offense’s TOI.
Two divergences can be seen when looking at the difference. The larger of the two happens on the negative side, meaning the offense has been out for a lot longer than the defense, but we also see it on the positive side, meaning the defense has been out much longer.
Both ends would suggest line shifts, the left being when the defense is caught changing and the right being for the offense.
It’s clear that TOI is in important part of a hockey game. Especially when it comes to offensive time on ice, the average xGoal value does increase, and continues to increase as the TOI gets longer.
Defensively though, there is not as much evidence to support if it truly makes a difference based on just the TOI numbers.
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