For the past few seasons, fans seem to think the St. Louis Blues have problems with showing up for the 2nd period. They might go up in the first but tend to lay back in the 2nd and lose the lead. It seems to be something that frustrates every Blues' fan, but should it? Is the 2nd period slump a real thing that has meaning or just something we notice when it happens but isn't a real trend?
I pulled all the score adjusted data from War on Ice for all NHL teams by period, and then the Blues score adjusted stats by period for every game so far this season. I chose score adjusted data, because we know that teams play differently depending on what the score is in a given period. By using score adjusted data we can control for that factor.
Looking at the Blues corsi for percentage broken out by period, it appears that the 2nd period has the worst corsi for out of all three periods of action. Okay, so this can confirm the "eye test" of many fans that the Blues are indeed not playing as well in 2nd periods this season. But, is the difference meaningful? How does it compare to the other teams in the league? When we take a look at the Blues score adjusted corsi compared to the other teams in NHL during the 2nd period, we see the Blues are one of the top teams in corsi for the 2nd period. Not only that, but their corsi for percentage falls within +/-1 standard deviation. This is a quick and dirty way to determine whether or not this is a typical result, and it is typical. But the big surprise to me was the Blues third period (you can sort each column in that chart by mousing over the CF% label at the bottom and clicking on the sort icon that appears). The Blues lead the league in score adjusted corsi for in the third period. It is just outside the +/- 1 standard deviation band, and their PDO for the third period is 102.2. Comeback kids with the magic ingredient for being clutch? This third period performance is not sustainable and it will be interesting to watch how this team performs in the 3rd for the remainder of season.
Has this been a problem that has plagued the Blues all season or a more recent trend? We can isolate the 2nd period by game and take a look at the trend over the course of the season. The Blues started the season maintaining a corsi for above their season average and above 50% through about 20 games. But then the 2nd period starts to trend downwards. However, when we isolate the 2nd period and compare it to the standard deviation for the league during 2nd periods the results tend to fall within that +/- 1 standard deviation band. So while we might have noticed a difference in how the Blues play the 2nd period, it falls within what we could consider to be typical and nothing out of the ordinary. However, if the trend continues, we could see more and more games with 2nd periods falling outside that standard deviation band which will indicate a significant problem for the team.
Let's take our look at the 2nd period one step further by examining what should be the ultimate result of corsi, goals. Here is the classic case of the Blues winning possession but losing the goals. Both first and second periods have below 50% goals for percentage while the third period is a whopping 66%! But that 2nd period goals for percentage places them within the bottom 10 teams for 2nd period (even if it is within the +/- 1 standard deviation band). Obviously a major problem for The Note. The 10 game moving average trend for goals for is also troubling. Both 1st and 3rd periods are slightly upwards, but the 2nd period trend is downward.
So do the Blues have a problem playing in the 2nd period? Yes, but it is a goal scoring problem (both for and against). They are managing puck possession, but their opponents are still finding ways to score on the Blues. Is this goal scoring problem real or just part of the normal ebbs and flows of the game? With a sub 100.0 PDO for the 1st and 2nd periods while still maintaining a good possession game suggests that the Blues are just not getting the bounces. Or it could mean they are making dumb mistakes that their opponents are able to take advantage of to score goals. I think it is a combination of these two things. Blues get unlucky bounces, but they also make mistakes that provide prime scoring chances for opponents. Whatever the reasons, Blues fans are noticing a drop in 2nd period play. The possession aspect of the 2nd period isn't the problem though, it is the goal scoring.