By Benjamin Wendorf – special to THN
As the fervor dies down from the fever pitch of opening games, NHL teams and their fanbases shift into the time-honored ritual of agonizing over early-season results. A few coaches begin to feel the walls close in, and regardless of testaments of faith by upper management, at least one will be fired in the first few months. Do teams carry out these decisions wisely? What kind of measures can help us determine if it’s a good move?
Reaching back to the THN Analytics stats primer, the best team measures we can use relate to regression and possession. For regression we can use “PDO,” or a team’s shooting percentage plus save percentage (for historical comparisons, I only use the first two periods to avoid the effects of “protecting” leads). It’s often expressed as a whole number like 980 or 1000, rather than their actual values of .980 or 1.000. Teams that are far above or below a range of about 990 – 1100 pull heavily (or regress) towards that range the remainder of the season. PDO is a great metric for this kind of study because its measure speaks directly to a team’s success in scoring or preventing goals.
Possession is currently best measured by Fenwick Close, but we can go further back in NHL history by using a team’s shots-for in the first two periods divided by both teams’ shots-for in those periods, called two-period shot percentage or 2pS%. It runs side-by-side with Fenwick Close, has a strong relationship with outscoring, and provides about 50 more years of data.
Using these two measures, we can look at a large body of coaching changes in NHL history. Through 140 coaching changes (minimum 20+ games for each coach), the before-and-after of PDO and possession is telling:
Historically, the changes have barely registered an uptick in possession (that 0.4% is worth a little less than one more goal-for), but that PDO shift would be good for about 14 more goals-for. In other words, NHL teams tend to cut bait when bad luck, not necessarily bad leadership, seemed to be the bigger problem. For comparison’s sake, I also put together a complete list of 97 coaching performances where the coaches had significantly low PDOs through the first 20 games but didn’t get canned: Read more