Bypassing the Shot Quality Argument: Were the 2012-2013 Leafs Lucky?

The true ability of the Toronto Maple Leafs seems to be the subject of never-ending debate in the hockey world. On the one hand, you’ve got the fancy stats crowd who insists that the incredibly high shooting percentages the Leafs have posted since the start of the 2012-2013 season can’t possibly be sustained over a long period of time, and that a crash back down to mediocrity is inevitable. On the other side of the coin, you have the traditionalists who claim that truculence, toughness, and creating and capitalizing on quality chances have driven the Buds to a renewed relevance in the Eastern Conference. Regardless of which side you lean towards, the debate over whether the Leafs are a lucky team or a genuinely good team rests on whether you believe that players or teams can sustain a high shooting percentage over the course of one or more seasons.

I’d propose, however, that we can evaluate the luck argument in a different way, without having to consider whether high shooting percentages can be sustained or not. By examining the historical shooting percentages of the players who played for the Leafs over the course of the last season, and then looking at who was taking the shots for the Leafs last year, we can get an estimate as to how many goals the Leafs should have scored, had they produced at the same rate that they had in the past. If the Leafs scored more goals last year than their historical shooting percentage would have suggested, than we can claim that the Leafs likely had lady luck on their side when they ended their 7 year playoff drought, while if the Leafs total goals for is in line with their past performance it would suggest that perhaps the Leafs really do possess an above-average ability to score goals.

I decided to approach the problem in two ways to get a sense of each teams expected goals for: first, I examined the individual stats for each player with at least 100 even-strength minutes over 2012-2013, and calculated the expected number of goals each player would have scored, given the players actual shot numbers and the shooting percentage they recorded between 2007 and 2012 (stats via stats.hockeyanalysis.com). Second, I took each players historical on-ice Corsi shooting percentage and found how many goals his team would be expected to score, given the number of Corsi attempts he was on the ice for. I then took the delta between each player’s actual and expected goals for, and found the total difference between actual and expected goals for each team using each method. In both cases I looked only at 5v5 shooting percentages, and at players with at least 100 5v5 minutes in 2012-2013. While it would be ideal to compare against historical powerplay performance as well, looking at only even-strength data should give us a pretty good idea of who did better than their historical numbers would have predicted.

The chart above lists each team’s total goals for delta using each of methods I described previously. Positive numbers indicate that a team scored more goals than their historical shooting percentage would have predicted, while negative numbers mean that a team underperformed their past shooting percentage. The results in the chart are pretty self-explanatory and sort of demolish the idea that the Leafs success can be credited to Dave Nonis putting together a group of strong goal scorers. In 2012-2013 the Leafs scored between 17 and 20 more goals than their historical shooting performance suggested they would have, the biggest delta of any team last year. The closest overperformer was the Tampa Bay Lightning who put up about 13.5 more goals than would have been expected, while the New Jersey Devils seemed to be the biggest laggard, scoring between 12 and 19 fewer goals than their track record would have predicted.

How much were those extra 17-20 goals worth for the Leafs? We can put together an estimate by reducing/increasing each teams Goals For by the amounts listed in the table above and then calculating their Pythagorean Winning % (the Pythagorean Win % is a simple method to estimate what a teams win percentage should be given their goals for and against, and is very strongly correlated with actual winning percentage). In the table below I’ve listed each team’s Winning %, Pythagorean Winning %, and Pythagorean Winning % based on historically adjusted Goals For.

When we bring the Leafs back down to their 2007-2012 shooting rates, their winning percentage drops from a respectable 54% (tied with Vancouver) down to around the 49% mark, which would likely have left them out of the playoff picture last year. The Minnesota Wild also appear to have been lucky in qualifying for the 2012-2013 playoffs, although their luck was more in outperforming their general Pythagorean Expected Win % than in scoring at a higher rate than we’d expect (The Wild’s GF rate was almost exactly in line with what we would have expected from their past shooting percentages).

I think these results basically point to three possibilities for the 2012-2013 Leafs:

1)      The Leafs were lucky to post such a high shooting percentage, and likely made the playoffs based more on luck than repeatable skill.

2)      The Leafs players underperformed their true goal scoring ability between 2007 and 2012, and finally realized their potential in 2012-2013.

3)      Randy Carlyle’s coaching system makes players better shooters and increases their shooting percentage above their historical rate.

Personally, only one of those 3 scenarios seems reasonable to me, and it’s not option 2 or 3. Regardless of where you stand on the whole shot quality argument, the Leafs definitely scored far more goals last year than their players’ past performance would suggest is reasonable. While the Leafs are sitting in a good spot atop the new Eastern Conference right now, I wouldn’t bet on their ability to keep it up-eventually the percentages are going to catch up with them and bring them back down to earth.