The Four Factors and Defense in the Big Ten

Nothing puts a discouraging bludgeoning in a crucial conference home game out of your mind like looking at a few soulless statistics. Here's my contribution.

Every game recap here on TOC (eventually) contains a four-factors graph, courtesy of StatSheet.com. Why? You can read the details in KJ's excellent primer (and the pages it links to) found on the sidebar, but, basically, the four factors explain a team's efficiency at scoring and allowing points, which is pretty strongly related to whether they win or lose.

But the importance of each of the four factors differs from team to team. Some teams, like Ohio State, specialize in minimizing the scoring opportunities they allow by keeping their opponents off the free-throw line. Others, like our Spartans, try to crash the offensive glass to create more chances to score. The perfect team would score well in all four factors, but in the real world not all teams are created equal.

How can you tell which factors are most important for which teams? Pomeroy has a page for each team called the game plan. Here's Michigan State's. Located at the bottom of the game plan is the correlation of each of the four factors to a team's offensive or defensive efficiency. These numbers give you a rough idea of how much of a team's efficiency can be accounted for by each factor.

The table below summarizes this information for each Big Ten team for defensive efficiency. Remember that defensive efficiency going "up" is a bad thing. You want the other guys to score fewer points per possession. So when the eFG%, OR% and FTR of opponents goes up, so does the defensive efficiency number. When the defense is forcing more turnovers, scoring goes down, in general, and so does the efficiency number. The correlation measures how strong that connection is for each factor. 100 (or -100) would be perfect correlation. Numbers close to zero indicate a weak or non-existent relationship. Rank is their national ranking in that factor.

I've indicated, with red and green shading a la Dan Hanner, some particularly interesting figures. Red is an especially strong connection and green an unusually weak one. A few things jumped out at me (after the jump):

• The most obvious takeaway is that how well your opponent is shooting (eFG%) is easily the largest factor in defensive efficiency. No team has a correlation lower than 67 here and no other factor anywhere in the table has a value higher than 70. KJ has covered this one thoroughly, most recently here. In the case of the Big Ten it seems that for a group of 6 teams it's especially critical, with values of 85 or higher.

• In fact, nothing really matters to Michigan's defensive efficiency other than whether their opponents' shots are going down. Their eFG% correlation is 88 and their correlations for the other factors are all weak and in the bottom five in the league.

• Minnesota has one of the more interesting numbers on this chart. Their defensive efficiency is explained every bit as well by the rate at which they generate turnovers as by how well their opponent is shooting. Since they play a lot of zone, this suggests that how their opponents are able to adjust to this uncommon defense has an unusually large impact on how well they're able to score. In fact, Minnesota has not lost a game where they forced the other team into a 20+% turnover rate and in those games only West Virginia had an offensive efficiency over 100 (111.5).

• They don't call fouls in the Big Ten. Except on Michigan State, Northwestern and Indiana. Indiana has a crazy and destructive addiction to fouling, but their number is always high. MSU has the strongest correlation between defensive efficiency and defensive FTR by a good margin. When they get whistled a lot, their defense suffers. The Spartans have had a defensive efficiency over 100 in 10 of the 12 games where they had a defensive FTR above 35. In their other games, defensive efficiency has been under 100 10 times. MSU's 5 highest defensive FTR games were all losses and only one referee, Jim Cahill, worked as many as two of them, so it looks more like an issue of loss of focus and corresponding poor execution than official persecution.

• Purdue's defensive efficiency, on the other hand, appears to be completely unrelated to how often they foul. Michigan State posted a 117 efficiency mark on them in the first meeting despite only getting to the line at a 21% rate and the Boilers throttled Ohio State (92.4 efficiency) while racking up a 61.7 defensive FTR.

• Wisconsin is tough to figure. Their strength of correlation for each of the four factors is in the bottom three in the league. None are above 70 and two are below 25. As an example of their defensive schizophrenia, Illinois put up two of the top 5 offensive games against Wisconsin this year. In the first game they had a 63.4 eFG%, 34.0 in the second. In the first the Illini turned it over 21% of the time and in the second 11.5%. They rebounded 32.5% of their misses in the first game and 40.8 in the second. The only relative constant was that the Badgers sent them to the line a lot in both games, accounting for two of the only three times Illinois cracked the 50% mark in FTR this year. But on the season, defensive FTR is Wisconsin's lowest correlation of the four factors. Go figure.

There's some equally interesting data to be mined in the offensive correlations. In my next post I'll take a look at those.