Did Tyson Barrie Steal Ryan Nugent-Hopkins's Assists?
Hat-tip to @SportsThor for the suggestion. On Tuesday, the Edmonton Oilers announced they had re-signed Ryan Nugent-Hopkins to an 8-year, $41 million contract extension. This year, RNH had an underwhelming offensive season, especially considering he spent most of it on a line with Connor McDavid, who put up one of the greatest offensive seasons in the history of the league. Still, most reasonable fans and pundits have acknowledged that letting RNH walk would have been, at the very least, a step backward for the team that they would have needed to match with at least an equally large step forward somewhere else. This is a difficult question to answer simply, because making a prediction about a players future performance has many components. That seems like an unusual question to ask. Barrie led NHL defencemen in points this year, and most NHL forwards would be licking their chops at the opportunity to play with the NHLs most productive defenceman in their contract year. From this point of view, you could conclude that RNH wears the responsibility for his down year; he had every opportunity to succeed on offence. Spending most of the season on a five-man unit with both the NHLs highest-scoring forward and defenceman should have been like winning the lottery, but RNH put up mediocre points-per-game numbers relative to past seasons:  At the very least, this season ended a run of three straight seasons where RNH racked up more points per game than the previous one. It seemed, until this year, like The Nuge was going to reach another level. It is especially troubling that he did not, given he played with the leagues highest-scoring forward and defenceman. But theres another possibility: Maybe the reason Barrie was the NHLs highest-scoring defenceman is related to the reason RNH had a down season in terms of point production. Specifically, maybe some of the assists RNH had been cashing in on in recent years (and sans-Barrie, would have cashed in on this year) were instead scooped up by Barrie this year. Testing the Theory  The way I think about it, there are two ways this could be true (and of course there could be more that I havent thought of). In both cases, what Im concerned with is the proportion of goals that get scored when RNH is on the ice on which he records an assist. That is, if Barrie is stealing RNHs assists, wed expect RNH to record fewer assists specifically for goals that are scored when he is on the ice. For the purpose of this post, Ill call it Assists per Goal. The logic behind this is, if we subtract Barrie from the equation, these are the goals RNH would have been more likely to record assists on, thus mitigating his down year. The first mechanism I see as a possibility is that RNH gets the puck to Barrie, and when the puck goes in, Barrie eventually records the secondary assist. That is, maybe a large portion of RNHs assists became third assists and no longer count on the scoresheet. This seemed plausible because of the large number of secondary assists Barrie recorded this season (27, which led all NHL defencemen). Lets look at RNHs Secondary Assists per Goal for each of his career seasons. If Barrie was specifically stealing secondary assists this year, wed expect RNH to show a substantial drop in Secondary Assists per Goal like we saw in points per game. This is not what we see. RNH actually recorded a greater proportion of secondary assists per on-ice goal this year than last year. He also recorded fewer in 2017. It is also true that this metric seems to be extremely noisy, or highly variable from year to year. In sum, I think it is very difficult to draw any sort of meaningful conclusion from this, but I think we can assume that it is not the case that Barrie caused RNHs secondary assists to become third assists. The second mechanism I see as a possibility is that Barrie gets the puck immediately to one of the Oilers most skilled players (Connor McDavid or Leon Draisaitl), who create a goal before RNH has a chance to get involved in the play. This would appear as a substantial drop in Assists per Goal (both primary and secondary) from last season, because RNH is simply not touching the puck as often on scoring plays. Heres his Assists per Goal for each of the seasons he has played in his career:  Theres certainly something there. RNH recorded by far his fewest career Assists per Goal this season. Remember that he played with Tyson Barrie only this season and none of his previous seasons. So, we cant rule out the idea that Barrie has stolen some of RNHs assists. But, it should also be the case, if Barrie is recording some of the assists that were RNHs in past seasons, we might expect to see a large increase in Assists per Goal for Barrie this season. This is extremely suspicious. From this graph alone, it certainly appears to be the case that Barrie stole some of RNHs assists. Barries Assists per Goal jump from last year to this year is almost exactly equivalent to RNHs drop in Assists per Goal. I think the conclusion from this is that, had the Oilers not signed Tyson Barrie, RNH would very likely have had a much more normal season, at least in terms of the proportion of goals scored while he was on the ice on which he recorded an assist. Following from that, you could certainly argue that RNH might see an increase in this metric next season (if Barrie is not re-signed by the Oilers), and beyond that, a return to form in terms of points per game. This is especially true if he logs any serious ice time with Connor McDavid and/or Leon Draisaitl, who have been 1-2 in league scoring for two seasons in a row. For this reason, it might even be reasonable to expect RNH to outperform his Assists per Game (and maybe his Points per Game) from two years ago. Some Reasons to Be Cautious  I want to preach caution for two reasons. To make a strong conclusion on this topic, youd want to be certain of (at least) two things. One, that this drop is driven primarily by goals scored when Barrie is on the ice with RNH, and not by goals scored without Barrie on the ice. If we want to pinpoint Barrie specifically as RNHs problem, wed need to be certain that RNH didnt also record very few Assists per Goal without Barrie on the ice. If that were true, maybe RNH just had a down season and is at fault for it. I have a scraper Ive used for NHL play-by-play data, but it seems to be missing too large a number of events (goals with RNH on the ice) for my comfort, and so I cant make an evaluation with any degree of confidence. If anyone has a working one, or knows where you can get such data (which players are on the ice for each goal scored and who recorded the assists), I encourage them to take a crack at this or we can collaborate on it. Two, wed need to be certain that the drop in assists/goal this season is more than we would expect by random chance. Its possible that RNHs down year is just a blip (and this is even more likely because it was a shortened season). Luckily, this is the type of analysis Im actually formally trained to do. I tried this several ways and I wont include all the details to avoid boring you (if youre interested, you can find those details in my code housed on my GitHub here), but I conducted a Bayesian t-test with a prior distribution scaled to the size of the difference in Assists per Goal from 2019 to 2020 for all NHL skaters. In essence, what this test tells us is how unlike the average 2019-2020 difference in this metric RNHs difference is. And the results of that test are almost perfectly inconclusive. That is, theres very little evidence that RNHs drop in Assists per Goal this year is any different than the drop experienced by random chance across all the leagues players. Conclusion  In summary, it certainly looks like Tyson Barrie stole a substantial number of assists from Ryan Nugent-Hopkins this year. It looks like this because RNH recorded by far his lowest career Assists per Goal, and the drop in this metric from last year to this year is almost perfectly matched by an increase in the same metric for Tyson Barrie. But, there are reasons to be cautious about that conclusion. As for what to expect from RNH next year, lets work off the assumption that the Oilers wont be re-signing Barrie. Id predict, based on what Ive detailed here, that RNH will likely be more involved in the goals scored when hes on the ice next season. And, given hes likely to record a lot of ice time with at least one of Connor McDavid or Leon Draisaitl, Id expect his points-per-game to increase next year as well. In other words, Im betting on Ryan Nugent-Hopkins to out-produce his contract next year. ___________________________________________________________  You can find me on Twitter @OilersRational. Ive made my code and the data I used (adapted from Natural Stat Trick and MoneyPuck) available here if you want to try running this analysis for yourself or tweaking parts of it. Im also available for help if you want to get into analyzing data but dont know where to start.