WNBA statistics: Why the Chicago Sky have improved on defense

If you'll allow me to ignore mathematical possibilities for a moment, the WNBA playoff picture is pretty much set: it's unlikely that the Phoenix Mercury will play their way out of the Western Conference playoffs and unlikely that the New York Liberty will play their way in at this point.

That leaves us some room to begin talking about playoff positioning and matchups a bit as teams jockey for seeding, but before we get into that let's lay the groundwork with some statistics. And there's one significant development to notice: the Chicago Sky have moved into contender range by crossing the +6 efficiency differential threshold.

Offensive and defensive efficiency for the WNBA as of 9/2/13. Full statistics at National Sports Rankings.

What's interesting about the Sky having such a strong differential - and being so far ahead of the next closest team - is that for most of the season there have only been two teams that rated as elite. Now there's a third. And those familiar with the old cliche about what wins championships won't be too surprised as to why they've risen: defense.

Looking at their Four Factors numbers, the Sky have been at or near the top of the league in scoring efficiency differential and offensive rebounding differential all season. But what's helped them since the All-Star break is that they've started to force more turnovers.

Turnover rates for the Chicago Sky and their opponents before and after the All-Star break as of 9/2/13.

That 5% increase in turnovers for their opponents represents a move from a team that forces among the least turnovers in the league to a team that forces among the most. The interesting thing about their improvement is that, unlike teams like the Atlanta Dream or Indiana Fever, they're not doing it with a few players that individually force steals.

There are two possible explanations for that, at the team and individual level. First, the Sky's frontcourt length that has helped the Sky hold opponents to a league-low 52% shooting from the 1-5 foot range, according to numbers made available by the Minnesota Lynx also helps them force opponents into bad decisions. Second, the Sky allow the lowest free throw rate in the league (25.7%), which means they're preventing opponents from scoring inside without the cost of fouling.

Either way, all signs point to the root of the Sky's defensive success being 6-foot-6 center Sylvia Fowles, who is making a strong case for winning the 2013 MVP award this season by doing it at both ends of the floor for the top team in the Eastern Conference.