Should Preds fans be worried about Pekka Rinne?

Source: USA Today

It goes without saying that Pekka Rinne is central to the Nashville Predators' success in the upcoming playoffs, given his $7M cap hit on the Predators' $60M payroll and 93.66% 5v5 Save % this season. But something has been off with Rinne as of late, with Rinne posting a sub-.900 Save % in his last five consecutive starts. While Predators fans shouldn't point to momentum alone as a reason to be concerned with Rinne headed into the playoffs (e.g., Jonathan Quick's final two games last season were both sub-.900 Save % efforts), there has clearly been a drop-off in Rinne's play. In the below chart, I split Pekka Rinne's 2014-15 5v5 Save % (both regular and adjusted based on average shot distance) into two halves of the season - before and after his knee injury on January 15th. 

Data Source: War-on-Ice.com

Is fallout from Pekka Rinne's knee injury accounting for this recent falloff?  One could look to the unsustainable play of the Predators' skaters as a cause, but Rinne's Shots Against per 60 minutes (SA60) are nearly identical for both halves of the season (28.07 vs. 27.94). Something else is almost definitely explaining why Rinne's Save % has dropped nearly two full percentage points since returning from injury. 

Now, it should be noted that we are of course dealing with sample sizes here: 37 GP / 1,770 Min for the first half and 27 GP / 1,317 Min for the second half, respectively. It's probable that luck played some role in Rinne's early season success, and that Rinne has simply regressed back to the mean. Rinne is a career 92.87% 5v5 / 93.19% Adjusted Save % goalie dating back to 2008-09, his first full season in the league. If we boil that down to his relatively healthy 2008-09 through 2012-13 seasons, the numbers are a bit higher at 92.94% 5v5 / 93.36% Adj., as Rinne played just 24 games in his anomaly of a 2013-14 season. 

Source: War-on-Ice.com

So while Rinne's second half performance is much closer to his career average than his Vezina-worthy first half was, it's not crazy to infer that the knee injury is playing a part in Rinne's recent falloff. After all, Rinne is a butterfly style goaltender, a style that contributed to his needing hip surgery in the 2013 offseason and likely helped induce this year's knee injury given the connection between the hip and knee. Granted if you were to ask David Poile or Peter Laviolette about Rinne's health, they would tell you that the goaltender is just fine. In any case though, when trying to predict Nashville's ability to progress past the Blackhawks and beyond in this year's playoffs, we should expect Pekka Rinne's play to be closer to the second half version than the first partially due to both his career numbers and his recent injury history.

When digging deeper into Rinne's 2014-15 season, I was struck by how different one advanced metric was between the two halves. A trio of statistics recently introduced by War-on-Ice that I find intriguing is the separation of saves into high, medium and low percentage scoring areas as shown in the below graphic:

Source: War-On-Ice

When we compare the two halves of Rinne's in the below chart, it is glaringly obvious where Rinne's game has fallen off since returning from injury: Medium scoring areas. As mentioned previously, we are dealing with somewhat small sample sizes here. But when it comes to shots from the left, right and high slots and center point, Pekka Rinne is having a much harder time stopping these shots now than he was in the first half of the season:

Source: War-on-Ice.com

Now there is almost definitely some bad luck going on here when it comes to Rinne stopping Medium area shots; the question is how much? It is worth repeating that Rinne's workload has not changed too much from the first to second half of the season. The Preds continue to average around 28 SA60 and medium shot opportunities accounted for roughly one quarter of Rinne's workload in both halves of the season. As Rinne's a 93.58% Medium Save % goalie for his career, a little bit of regression was to be expected here; however, Rinne's second half is much further from his career average than the first with respect to Medium Save opportunities:

Source: War-on-Ice.com

While it's probable that Rinne's Medium Save % trends back upwards, it's worth noting that Rinne's only other season where he was this low in Medium Save % opportunities was last season's hip injury-riddled season. Furthermore, 2014-15 now ranks as Rinne's second worst season for Medium Save opportunities by a large margin after being on pace to be his best year in the statistic through 37 games. Compared to his peers, Rinne's overall Save % in the second half of the season still rates him along the lines of an average NHL goaltender such as Marc Andre Fleury or Jaroslav Halak. But among 33 goaltenders that played 1,300+ minutes this season, Ryan Miller was the only goaltender with a sub-.900% Medium Save %, placing the recent version of Rinne at the very low end of the playoff goaltending spectrum in that category.

So while we can't definitively link Rinne's drop in Medium Save % to his recent knee injury, it's worth exploring in future research whether a link can be established between lower body injuries and a drop-off in Medium Save % for goalies. In theory, medium opportunities could be where goaltender health and skill and most differentiable. After all, High Save % opportunities are largely based on goaltending fundamentals than differentiable goaltending skill and health, while Low Save % opportunities have a lot more luck involved due to the shot proximity. 

So how concerned should the Predators be? While there should be more room for optimism in Nashville than other markets due to the Laviolette-coached Predators' improved ability to drive possession through multi-shot shifts, the team should at best expect Rinne to play at his career averages. Perhaps that could be enough, as this year's Blackhawks only scored on 7.62% of shot attempts. However, Rinne's recent play (not to mention the probable return of Patrick Kane for Game 1) could very well help the Blackhawks regain their goal scoring clip of 9-10% from the previous five seasons. Whether it's a function of injury or not, Pekka Rinne's play will definitely be one of the top storylines to follow in the NHL's opening playoff rounds.