Thread: Candace Parker serves as an interesting case study on defensive evaluation. My Estimated Contribution metric values her defense this season at +1.4 points per 100 possessions, a top-5 mark. But, as always, it's important to dig deeper into it. https://positiveresidual.com/shiny/wnba/ 

First, whenever we're talking about all-in-one metrics, we have to remember that there's error associated with them. Estimated Contribution is no different. So we shouldn't just "let the number speak for itself." Rather, we should use it as a starting point for analysis.

Estimated Contribution consists of a box score component and an on-court/off-court component. Candace Parker's defense stood out in the box score component, where she was atop the WNBA at +1.7. Within this category, there were a few places where her performance was noteworthy.

Adjusting for pace of play, Candace Parker averaged 11 defensive rebounds per 40 minutes. Only Amanda Zahui B had a higher rate among players with at least 250 minutes. Now, rebounding numbers can sometimes be inflated, but Parker's output seemed to be impactful.

When Candace Parker was on the court, the Sparks had an above-average 79% defensive rebounding rate. When she was off, they were down to 67%, 9 percentage points below league average. That could be a function of LA's reserves, but it strikes me that there's signal to the numbers.

Furthermore, Candace Parker's among the handful of players who averaged at least 1.5 steals and 1.5 blocks per 40 minutes when adjusting for pace of play. This highlighted her defensive versatility and helped boost the box-score component of her Estimated Contribution.

It gets a bit more interesting when we shift to the on-court / off-court component of Candace Parker's numbers. At first blush, it looks promising. When she's on, the Sparks average a 96 defensive rating. When she's off, it worsens to 102. https://stats.wnba.com/team/1611661320/onoffcourt-summary/?Season=2020&SeasonType=Regular%20Season&sort=DIFF_DEF_RATING&dir=-1

However, there are some key things to be mindful of when it comes to on/off data. First, they can be noisy -- subject to random variation in 3-point and free throw shooting. This is why you often see analytics folks talk about adjusting for "luck."

The on/off tool in the WNBA Dashboard includes "luck-adjusted" ratings. When we look at Candace Parker's numbers, we see that the Sparks' defensive rating is at 97 while she's on the court -- comparable to their standard rating. Off-court numbers are different, though.

When adjusting for random variation in opponent 3-point and free throw shooting, the Sparks average a 96 defensive rating while Candace Parker's off the floor -- much lower than the standard off-court defensive rating and roughly comparable to the luck-adjusted defensive rating.

So there's evidence to suggest that Sparks lineups without Candace Parker may have suffered some bad luck on the defensive end. That means her impact *may* have appeared larger than it truly was. It doesn't discount her accomplishments entirely, but it's something worth noting.