Shooting percentage was one of the statistics that explained what afflicted the 2017-18 Chicago Blackhawks. Most notably, Jonathan Toews and Brandon Saad converted shots into goals at a rate that was well below their career averages.
With the 2018-19 Blackhawks also struggling to win games, it’s worth exploring a statistic that examines a similar part of the game that can help explain what’s not going right for this year’s Hawks: PDO.
What is PDO?
PDO is an acronym for “Percentage Determined Outcomes.” This statistic is the combination of a team’s shot percentage and save percentage, typically measured at even-strength. For example, if a team scored three goals on 30 shots in one game (10 percent) and allowed two goals on 25 shots (92 percent, or .920 save percentage) against during a 3-2 victory, the winning team’s PDO would be 102 and the losing team’s PDO would be 98.
Though teams can stray away from the average PDO mark of 100, over longer periods of time, the numbers always revert back towards 100. The conventional wisdom on this statistic suggests that it’s a way to measure luck, that teams with a PDO well over 100 are getting all the bounces, and teams in the mid-90s are not.
However, this statistic can also point to how skilled a team is. A top NHL team will likely have a goaltender with a save percentage above league average, and will also contain multiple skaters who can score goals at a rate higher than most. Because of that, the team’s save percentage and shot percentage will add up to a number higher than 100 because that team has higher-skilled players — and vice-versa. For example: the 2012-13 Blackhawks had a PDO of 101.9. That team had the league’s best record and won the Stanley Cup. The 2017-18 Blackhawks had a PDO off 99.1. That team did not win a Stanley Cup. Or make the playoffs.
A worthwhile guide to PDO extremes is that elite teams will probably approach a PDO of 102, while the league’s worst teams will bottom out around 98. Any team above or below that range is likely due for a progression or reversion to the mean of 100 because they’re playing at a level either too good or too poor to continue.
Let’s munch some numbers
As of Tuesday morning, the Blackhawks sit at 25th in the league with a PDO of 98.55 (per Corisca). That sounds about right for a team that has had some spurts of offensive prowess but has a pair of goaltenders who are routinely left hanging by atrocious in-zone defense.
Using charts obtained from Sean Tierney’s outstanding website, complete with data compiled by Corsica, here are a few visualizations of the Blackhawks PDO numbers this season. The first graphic is league-wide breakdown of PDO. The Toronto Maple Leafs own a league-best mark of 103.26, while the San Jose Sharks are in the basement at 96.61, which might explain some of the struggles from that loaded roster.
The second image focuses specifically on the Blackhawks, with a rolling 5-game average of PDO. Chicago’s PDO bottomed out on Nov. 10 after a 4-0 loss to the Flyers, the seventh defeat during the Blackhawks 8-game skid.
Chicago’s five-game average at that point was 93.38, a number too low to last, and the Blackhawks returned to a more appropriate figure over the ensuing weeks.
So what do these numbers tell us?
A PDO under 100 suggests that the Blackhawks are victim of either bad luck or poor play. Considering how often players have been left all alone in the slot for prime scoring chances against Chicago’s goaltenders, the PDO confirms what anyone watching this team consistently has learned: this team’s overall defensive play has resulted in far too many quality scoring chances against. And this porous defense has affected the save percentage of every Blackhawks goaltender, ultimately lowering the team’s PDO into the range occupied by teams struggling to win games.