by | Jun 23, 2024 | 5 comments
This is follow-up to a recent Sound Of Hockey article where we sat down with the Seattle Kraken Ice Breakers to better understand the role they play at Kraken games. There was one question around the science behind scraping the ice that got me wondering how much of an impact ice scrapes have on NHL games, so we are going to dig into the statistics of goals scored following ice scrapes to see if we can uncover anything interesting.
Here was the question:
Kevin Ruuhela: If there is a science to it, I’m not aware of it, but from personal experience playing hockey since about the age of six, I know that the puck moves much more smoothly and consistently on ice without snow. When there are patches of snow, the puck can sometimes abruptly change speed on you and throw you off. I also know that goalies typically prefer less snow so there’s less material to get in their eyes from sticks and skates as players move around the crease.
To summarize Kevin’s answer and take it a bit farther, I came up with the following very simple theory:
Playing on smoother ice should increase scoring.
Let’s see how the statistics align with this theory.
For this data analysis, only even-strength goals (five-on-five) were reviewed. This removes any advantage a team might have and focuses on an even playing surface. Ice time was separated into two buckets:
150 seconds was chosen because, per Ruuhela, there are three planned ice scrapes during each period. Since each period starts with freshly Zambonied ice, there are a total of four fresh ice events. Two minutes and 30 seconds (or 150 seconds) multiplied by the four fresh ice events equals 10 minutes of fresh ice and 10 minutes of rough ice per period. Assuming there are no advantages given to teams during even-strength play, goals should be scored at a linear rate to the time on ice.
Here is a breakdown of how a period splits into the two buckets of ice:
In reality, ice scrapes are delayed or missed, so the actual percentages of time on fresh versus rough ice are not exactly 50 percent each. Actual percentages came out to 46.86 percent for fresh ice and 53.14 percent for rough ice.
Data was analyzed for the past three seasons for all NHL teams. In total, 3,936 games and 16,250 even-strength goals were reviewed.
To prove the theory, there should be more fresh ice goals than rough ice goals. What the data shows is the opposite, and a reduction in goals is observed following a fresh ice event.
The above chart is a bit hard to interpret, so let me try to provide some context. It is showing that 34.36 percent of the game, the ice is fresh following an ice scrape, but only 31.10 percent of goals are scored during this time. On the other hand, the ice is rough 53.14 percent of the time, and 56.52 percent of the goals are scored in these periods. Goal scoring on freshly Zambonied ice is almost linearly equal with 12.50 percent of the time accounting for 12.38 percent of the goals.
The total for fresh ice time is 46.86 percent of games, and 43.48 percent of 5-on-5 goals are scored during these periods.
Overall, there was a 6.76 percent swing between fresh ice scoring and rough ice scoring over the past three seasons. This means offense is up when the ice is rough and down after a fresh ice event.
Here are the raw data:
Remember, this is only looking at 5-on-5 goals, so no empty netters or power-play goals are included. Seeing that goal scoring is down following a fresh ice event got me thinking about goalie save percentage. Following similar logic, I analyzed the shot data for the 2023-24 NHL season to calculate league-wide goalie save percentage for even-strength play on rough and fresh ice.
Sure enough, the goaltenders see a boost in save percentage following a fresh ice event. I am speculating here, but for similar reasons we theorized that scoring would be up due to smoother ice. The goaltenders could be even more of a benefactor of smooth ice, as puck movement is more predictable.
This was a fun project, and I was surprised by the results. There is probably more to dig into here, because one thing I thought of is that even after a scrape by the ice crew, the playing surface is certainly smoother at the beginning of a period and following resurfacing than it is at the end. So, perhaps all “fresh” and “rough” ice is not created equal.
Still, in all my years of watching and playing hockey, I have always thought the opposite to be true, that when the ice had received some sort of attention either from the ice crew or from the Zamboni, teams would score more. There was a lot more data collected than presented here, but to quickly summarize it, shots, turnovers, various fresh ice time intervals, and regulation goals in all situations were factored in and showed the same result. There is a reduction in scoring and a boost to goaltending save percentage following an ice scrape.
If you have any questions or thoughts please comment below. You can follow @blaizg on x.com.
Interesting data. I am now thinking that the rest time for the players prior to fresh ice gives them the energy to defend better.
Great take on this but I wonder if you’re looking in the wrong direction. It would be interesting to see the stats on the average time to score after a face off. My thought is that by the time a team takes possession develops a forecheck etc. that it offsets the “fresh ice factor, I believe that the fresh ice definitely helps but they are playing on fairly fresh ice all game long with all the scrapes it gets it never gets that bad.
Interesting thought on average time to goal after a faceoff. Might be a future thing for me to look at.
With NHL players and how sharp their skates are, the ice gets chopped up quicker than you would think.
And then there’s that too!
I do think it matters but not in regards to the Zamboni philosophy. My reasoning is multi-facited. Bad ice make for more mistakes and bad bounces. Snow on the boards, creates craziness. Craziness creates havoc and mistakes in the “thats unfortunate” category. Hockey rinks: some rinks have better ice while others fall in to the sldge catergory and the ice get worse as the game goes on. Climatee change sort of as some cities have higher heat tempetures as opposed to others in a cold zone like moutains and Canada. Finally, the time of year which can coincide with outside tempeture. Fortunatelly, we do not see games played in fog anymore. Also, what about the outdoor games? All said and done, those stats are right on and make a lot of sense if the game was played on a stat sheet. Its played on ice and even with modern technology, there is always a margin going to the “OH sh*t” situation or the “Tooth Fairy” did it.
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