2020 NBA Free Agency: Does signing Robin Lopez actually make sense for the Wizards?

Reaction to the Wizards using most of their midlevel exception to sign free agent center Robin Lopez was swift and negative, including from me. But as the dust settles on Washington’s somewhat befuddling 2020 dive into free agency, I wanted to take a deeper look to determine if a) they’re seeing something I overlooked, and b) could I at least understand what they’re thinking, even if I don’t agree.

The Wizards’ decision to sign Lopez appears to be founded on three key stats:

1. He led the NBA last season in defensive box outs per 48 minutes,
2. Among players who appeared in at least 25 games, he was fourth in at-rim defensive field goal percentage, and
3. When he was identified as the defender, opponent effective field goal percentage declined by 3.7% last season, which was among the top 20-25 in the league.

Focus on just these three things, and it’s easy to understand what Tommy Sheppard and his advisors visualize: a physical big man who boxes out, protects the rim and lowers opponent field goal percentage. Bonus features: Lopez is wicked smart and funny, and he’ll ride Thomas Bryant to become a box out champion.

The problem: the big picture and confounding details.

While Lopez isn’t a prolific rebounder on his own, the theory goes that his box outs permit teammates to swoop in for easy boards they wouldn’t otherwise get. By preventing his man from getting the offensive board, he improves team rebounding.

That does show somewhat in the numbers. Last season, Milwaukee’s defensive rebounding percentage fell 2.1% when Lopez was on the floor, but team rebounding was better with him out there the preceding four seasons (three with the Chicago Bulls and one with the New York Knicks).

The effect was modest — +1.5% on the defensive boards over the past five seasons, and +2.0% if we leave out what he did with the Bucks last year. Improve the Wizards defensive rebounding by 1.5% would move them to 19th last season; by 2.0% they go to 18th.

The second and third stats cited above are iterations of the same thing: lowering opponent shooting percentage. As I’ve written many times, the team with the better effective field goal percentage wins about 78% of the time. If you want to have a good defense in the NBA, the data show the most important thing is making the other team miss. Lopez lowers opponent field goal percentage at the rim and when he’s defending, so he helps improves the defense. That’s the theory at least.

The actual data shows that over the past five seasons, Lopez’s teams have improved their defensive effective field goal percentage by 0.003 when he’s on the floor. Improving by that much would leave the Wizards 29th in defensive eFG — but contending for 28th.

Here’s the change in team defensive eFG over the past five seasons for Lopez’s teams when he’s on/off the floor:

• 2019-20 — MIL — +0.001
• 2018-19 — CHI — -0.028
• 2017-18 — CHI — -0.017
• 2016-17 — CHI — +0.004
• 2017-18 — NYK — +0.018

The best read of these data is that Lopez does not significantly impact his team’s ability to force missed shots.

Lopez does have impact in other areas, but on balance they haven’t been positive. When he’s on the court, his teams’ defensive turnover percentage has fallen each of the past five seasons (by an average 1.8%). The steals rate has also dropped by 1.1%. Blocks percentage has gone up slightly (0.4% over the past five seasons; 0.8% if we drop last season), but as mentioned above, without making a dent in opponent shooting efficiency.

What matters, of course, is the bottom line — team defensive rating (points allowed per 100 possessions). That’s not a positive for Lopez either — his teams were better defensively with him on the court in 2017-18 and 2018-19, but about the same (or a bit worse) in the other three. Here’s the change in his teams’ defensive ratings over the past five seasons with him on/off the floor:

• 2019-20 — MIL — +2.6 points per 100 possessions
• 2018-19 — CHI — -2.9
• 2017-18 — CHI — -4.0
• 2016-17 — CHI — +0.6
• 2017-18 — NYK — +1.6

Over the past five seasons, Lopez’s teams have been about half a point per 100 possessions better defensively when he’s on the floor. If we throw out last season because he didn’t get to play many minutes with Giannis Antetokounmpo or his brother, that number rises to 0.8 points per 100 possessions.

All this leads inexorably to the conclusion that Lopez is not an impact defender. Turning to other metrics such as the defense part of PPA, Jacob Goldstein’s PIPM, ESPN’s RPM, or other adjusted plus/minus metrics doesn’t change things. Each of them pegs Lopez as an average to below average defender.

I could turn to the offensive end of the floor, but it would only make the decision to give Lopez the MLE look worse. The Wizards signed him for defense and rebounding, and my read of the data suggests their decision involves some magical thinking.

One other likely reason behind signing Lopez — his reputation for meaningful off-court contributions. Here’s a terrific article from former NBA executive Ben Falk on what Lopez brought to the Portland Trail Blazers.

The Wizards surely have additional player evaluation tools, and maybe their evaluation is driven by something other than what I’ve discussed. But, upon further review, my conclusion remains the same as my first reaction: signing Lopez is a poor use of the team’s limited player acquisition resources. At least it’s for just one season.