The Tampa Bay Lightning are into the second half of their season and firmly positioned as the best team in the NHL. They lead in standings points and goal differential. They are one of the best teams in the league in 5v5 shot metrics. They have a dominant power play and a competent penalty kill.

For anyone involved with the team, this is an exciting time. But this isn’t the first time the team has looked this good through the halfway point. They did almost the same thing last year. But things changed in the second half of the season.

To see just how similar things are this season and to try to understand what happened last season, we’re going to look at some numbers. All data in this post is via Corsica and is adjusted for score and venue (home/away). All stats are standardized to be per sixty minutes of ice time.

To start, below are twenty game rolling averages of goal and expected goal differentials at both 5v5 and all situations for the last two seasons.

This chart establishes precisely where the trend changed last year. It occurred at almost the exact point in the season where we are now. The team’s goal and expected goal differentials dropped significantly from about games forty to sixty. The team started to play worse and got worse results.

But around game sixty, the team started to play better again as evidenced by their increasing expected goal differential. Their results did not change in same way. They continued to get worse goal results despite their improving play.

That brings up the question of what caused the weaker results to continue longer than their expected goal numbers would suggest they should have. The chart below is similar to the one above but shows only defensive play and results.

This tells the story cleanly. In the beginning of the year, the team was giving up less goals than expected, which means they were getting strong goaltending. Around the forty game mark, that started to change. The goaltending got progressively worse along with the defensive play and didn’t improve until the end of the season, which was well after the defensive play got back to normal.

To make sure the issue was mostly defense and goaltending, we can check the offensive numbers in a similar way.

The offensive numbers are consistent through the year with some small fluctuations but nothing like the peaks and valleys we saw in the defensive play.

In total, the story is clear. Last season, the Lightning were the best teams in the league through the first half of the season. During the second half of the season, the defense played worse and the goaltending struggled. That led to allowing more goals and winning less games.

So far this season, the Lightning are repeating their effort from last season. The process has been slightly different. The goaltending hasn’t been as good, partially due to Louis Domingue starting a stretch of games while Andrei Vasilevskiy was hurt. But Vasilevksiy himself hasn’t been as good this year either.

To compensate for the lesser goaltending, the offense has been unreal. The team is generating more expected goals than last season and outperforming that number by an even wider margin than last season. They’re scoring a ton of goals and that’s a big part of why they’ve won so many games so far this season.

The question will be whether the team can sustain this performance over the second half or whether they decline like they did last season. The goal scoring should slow at some point. That’s to be expected. What we should be more concerned about is whether the expected goal numbers on both offense and defense remain as impressive as they have been. Seeing Vasilevskiy put together a strong second half would also alleviate some concern over his ability to perform more consistently.

One difference from last year is the team’s depth. The coaching staff is rotating through seven defenders with Slater Koekkoek as the eighth player on the blue line. The forwards are so deep that when the team is fully healthy, a good player is sitting every night.

One side effect of this kind of depth could be that players feel more pressure to maintain their spot in the lineup and maybe, the team won’t be as prone to dips in performance because of that. This doesn’t stretch to the players at the top of the lineup but the constant competition for minutes at the bottom of the lineup could insulate the team from the natural dips in intensity during the regular season that come from being focused on the post season.

The Lightning have already shown they can be a great team. Just like last season. The question is whether they can sustain this level of play. The post season is a crapshoot. Being the best team in a seven game series doesn’t guarantee anything. But if the Lightning can avoid the sludgy play from this time last season, they’ll put themselves in the best position possible come the playoffs.