How does one measure a player’s impact on her team?
Is it by how many points she scores? How many assists she records? What percentage of her team’s total stats she accumulates?
This stuff has been available at WNBA.com for quite some time, but what’s been lacking is on/off court data. Just because a player doesn’t put up gaudy box score statistics doesn’t mean she isn’t contributing, and we can now see the extent to which teams are better or worse when each of their players is on or off the court.
Let’s take a look at the Las Vegas Aces, for example. You can find on/off court data in the same way as any other stats.
You should get something that looks like this. Now, technically, this is just a subset of the team page itself (just added as a shortcut in the navigation bar — how nice of them!), so you can scroll up and get back to the team profile, stats, players and so forth.
There’s a lot going on here and it can seem confusing at first. So let’s pick a player to use as an example. Take a closer look at Dearica Hamby’s numbers on this page:
There are several levels to be aware of here. Notice how the chart is split into columns: offensive rating (points scored per 100 possessions), defensive rating (points allowed per 100 possessions) and net rating (the difference between offensive and defensive ratings). These are then split into the player’s ratings for the minutes she is on and off the court.
So, in Hamby’s scenario, the Aces have scored roughly 101.2 points per 100 possessions with her on the court, but just 91.1 points per 100 possessions with her off the court, for an offensive rating differential of 10.1. The Aces have also been better defensively with Hamby on the floor than with her on the bench, allowing 8.6 fewer points per 100 possessions.
Now look back at the chart for a minute. The on-court net rating (highlighted in green) is the same figure as the one you can find on the player’s page under “advanced splits.” This stat is based on the number of points per 100 possessions the Aces are better than the opponent with Hamby on the floor: 16.9.
The other side of the coin is what’s highlighted in blue: The Aces have been outscored by 1.8 points per 100 possessions with Hamby off the court. Combine that with her on-court net rating, and you get her net on/off differential: 18.7 points per 100 possessions. As you can see from the chart, that’s comparable to Liz Cambage’s on/off court splits.
The Aces have clearly been better with Hamby on the court than with her on the bench, so let’s look at more stats and figure out why that is. On/off court data is also available for individual stats, so we can get some player-based context for those team-based ratings we just looked at.
Go to the top of the page and change “Summary” to “Four Factors.” The four factors include advanced stats that are strongly correlated with winning basketball (see the WNBA Stats FAQ for more information), so it’s a quick and effective way to gain the context we are looking for. It will look something like this (minus the highlights, of course):
Focusing on Hamby’s on/off splits here, we can easily see where that impressive net differential comes from. Not only are the Aces more efficient at shooting the ball when she’s on the court (as measured by eFG%), opponents’ shooting takes a sharp hit as well. Las Vegas is also better on the offensive glass (OREB%) when Hamby is on the court than they are when she’s off the court.
Context is important!
So that gives us a little more insight, although there are a few things we need to be careful of when looking at on/off numbers.
Obviously, basketball is played with five players at a time, not one, so it’s impossible to point to any one player’s on/off stats and say, “Player X is making Team Y better.” WNBA Stats has team lineup data available — which we’ll be looking at in the future — so comparing how a team does with different lineups and one player as a constant in those lineups would probably be a better option if you’re looking to get specific.
Also, beware of sample sizes! Hamby was a good choice for the purpose of this article because, thus far, the Aces have played 279 minutes with her on the court and 286 minutes with her off the court. That’s about as close of a split as you’re going to find. If you were to evaluate, say, Ji-Su Park’s play instead, on/off data probably wouldn’t mean as much.
Finally, take into consideration who the player is playing against while the data is being recorded. Again, Hamby was a good example here because she plays plenty of minutes against opponents’ starters and reserves. Players who see most of their minutes during garbage time might not have the most useful on/off splits.
Ultimately, though, this is fun data to look at, and certainly offers an additional perspective while watching games. Here are a few more players who have been indispensable to their respective teams — some of them might surprise you!