2014 midseason WNBA statistics: The Phoenix Mercury's dominance, the Minnesota Lynx's potential

When the Minnesota Lynx finished off the San Antonio Stars on Thursday night, the WNBA officially hit the midpoint of the season having played 102 of 204 scheduled regular season games and officially crossed the halfway mark after the L.A. Sparks dispatched the Seattle Storm at KeyArena.

That makes now about as good a time as any to post our (sort of semi-)weekly stats post looking at team performance. And although this isn't always the case, the numbers do highlight a few things that aren't immediately evident in the standings.

The efficiency differentials: A one-team elite

As I've described before, efficiency differentials - the difference between the number of points per possession a team scores and the how many they allow their opponents - has been a pretty good way to determine the teams we should consider contenders for a title.

And right now, there's absolutely no question that the Phoenix Mercury should be considered the best team in the league by a somewhat significant margin.

Table 1: 2014 WNBA efficiency numbers at mid-season (via Basketball-Reference).

It should come as no surprise that the Mercury are at the top here: they've won a league-high six straight and have the league's best record. Nevertheless, the numbers do give us a more concrete sense of how much better they have been than the rest of the league to this point.

We've already put a spotlight on how good the Mercury have been a few times this season - and will have another mid-season report forthcoming - but to put those numbers in perspective, +6 can generally be considered contender status as we've discussed previously; not only are the Mercury well above that threshold for being considered "elite", but there's also a somewhat significant gap between them and the rest of the league.

That gap is particularly stark in the context of this season because the three elite teams are the only teams that own a positive efficiency differential at all thus far, which suggests that it might be less accurate to say that the Western Conference is loaded than that the "middle class" of teams (very good, sub-contenders) has been squeezed out for some reason. There are probably some pretty simple explanations for that - injuries to teams that we might expect to be near the top and the L.A. Sparks' mind-boggling lack of consistency - but a gap that big is still noteworthy.

However, more interesting about this list is what might obviously change in the second half of the season.

I've hedged about the Mercury's dominance above with phrases like "somewhat significant" and "to this point" because the Minnesota Lynx have also been very good thus far and have yet to play a game at full strength: currently, starting power forward Rebekkah Brunson has yet to play a game and starting wing Seimone Augustus has missed three of the last six. Given how well rookie Damiris Dantas has played, this team could very easily be better than last year's at full strength. And despite the injuries to multiple players throughout the first half of the season, they're still just 0.5 games behind that Mercury team with the dominant numbers. Does a healthy Augustus and Brunson make up for that difference? Not to take anything away from the Mercury, but I'd fully expect the Lynx to take a statistical leap at full health for one reason: rebounding.

Four Factors statistics: Where the defending champs have room for improvement

Table 2: Four Factors statistics for the WNBA as of July 3, 2014 ordered by "OReb%" (via National Sports Rankings).

With Brunson in the lineup over the past three seasons in which the Lynx have won the Western Conference title, the Lynx have had among some of the best rebounding teams in league history.

In 2011, they had the best defensive rebounding percentage in league history at 76.5%. They weren't all that far behind that in 2012 and 2013. As you can tell from their opponents' offensive rebounding numbers above, they're rebounding at a slightly lower rate defensively. But their offensive rebounding has really taken a hit this year.

Since 2011, the Lynx haven't had an offensive rebounding percentage under 29.9% (2013). They led the league in 2011 (32.8%) and 2012 (34.7%) and were the best in the talented Western Conference (29.9%) last season. Not only have they fallen well short of that this season (as you can see in the table above) but they're also below the current league average of 27.98%. The obvious result: less second chance points, where they've fallen to third-worst.

Brunson might not explain all of that decline in rebounding - Devereaux Peters has recovering from offseason surgery for much of the season as well, leaving them with rookie Damiris Dantas as the starting power forward with a lower rebounding rate - but it's reasonable to assume that her absence has some impact on those numbers.

There has been some pretty cool work on how individual NBA players impact a team's offensive rebounding percentage, including the value of contested vs. uncontested rebounds. We simply don't have nearly the same data (publicly) available for the WNBA, but it probably wouldn't be too controversial to suggest that Brunson has a pretty strong impact on an entire team's rebounding profile. Brunson is the best active offensive rebounder in the league right now with an uncanny ability to track the ball off the rim and the athleticism to secure the rebound. You just can't replace that. And if the Lynx return to the levels they've been at for the last few years with her in the lineup, it's not really a stretch to assume that offensive efficiency number - currently third in the league, by the way - will improve.

Nevertheless, we can't just ignore what the Mercury have done this season and assume it will be easy for the Lynx to supplant them as the top seed in the Western Conference. Every study done on basketball statistics pretty much ever (that's not an exaggeration, to my knowledge) has shown a strong relationship between shooting efficiency and winning. So although Table 2 is ordered by offensive rebounding percentage, you might have noticed that the Mercury have both the highest shooting efficiency (53.10%) and the lowest opponent shooting efficiency (44.80%) in the league - both by healthy margins.

We've probably come to expect that kind of offensive performance from the Mercury, but that kind of defensive effort is almost unheard of in Phoenix (NBA or WNBA). The explanation should be pretty easy: Brittney Griner.

The Griner Effect

You hate to oversimplify defense with any one statistic, but the Griner Effect is real just from watching the games and it's hard to dismiss the story the numbers are telling. The Mercury have allowed the lowest 2-point percentage in the Western Conference this season (44.3%) and the lowest percentage in the league from 1-5 feet (52.3%) - it doesn't take complicated statistical research to know that a 6-foot-8 shot block significantly influences 2-point percentage.

With opponents struggling to score efficiently inside the arc, they have retreated to the three point line and not fared particularly well from there either: Mercury opponents shoot the second most threes per game (17.53) and hit the third-lowest percentage in the league (30.8%). So despite the Mercury's other defensive shortcomings, they're able to limit opponents' potency.

Is all of that because of Griner? Not really - she needs help on the perimeter for opponents to shoot that poorly from three point range. But when looking at how opponents score 15 points less per 40 minutes with Griner on the floor, it's also impossible to deny her defensive impact.