What is on/off, and is it a good stat?
On/off is a players net rating per 100 possessions minus the teams net rating when that player is not on the court. For example this past year, George Hill in 60 games had a +6.6 net rating and his teams were -1.9 when he was off the court, for a total of +8.5. Of course he spent 47 games with the Buck's. With the Buck's he had a 10.8 net rating when he played, and when he did not the Buck's were an impressive +7.8 for a total of +3.0 (7th best on the team right after Middleton with a +3.1).
But what does that mean (if anything)? And is this a good measurement? Opinions my vary on the question, but in my opinion, in small sample sizes, on/off is a very wonky. Issues like having a good/poor bench, better teammates can lead to a lower plus/minus, strength of schedule, luck, coaching staff and scheme (Lopez and the drop zone), injuries etc..... all can play a role in skewing the numbers. And of course past performance does not guarantee future performances.
I would never use it to say the player X is better then player Y because one has a higher on/off. For example, Stephen Curry has a career +12.1 on/off and LeBron James has a +11.4 on/off. I think it tells us that both players are great, but it is not the final answer.
However, as the sample sizes get larger, a clearer picture forms. There are some advantages to plus/minus as compared to just net rating. It is hard to compare a net rating from a player on two different teams because their teams net ratings will not be the same. By definition, the average on/off in the NBA is 0 and thus makes comparisons easier.
On/off also might catch some of the hidden traits of a player that does not show up in common stats like bbiq, screening, boxing out, defense in general, gravity, communication, on court leadership, moving without the ball, hustle and vet savvy (ex. how Horford knows how to hold). In a larger sample size, it helps answer the question of how much does a player helps his team win.
This past season, the median plus/minus for players on the the All-NBA team was +6.5. Remember George Hill had a +8.5 plus/minus combined as Cav/Buck. I am not saying Hill is an All-Star, but it is an impressive number. Paul George had the best with +15.9, Giannis had +9.7, and Blake Griffin had the lowest plus/minus of any All-NBA player with +2.2.
When looking closer at the big picture of plus/minus, some trends start to appear. Younger players struggle in plus/minus (that lack of vet savvy starts to show). Below is a chart of the median plus/minus of the top 9 players in minutes played.
1st year players -2.5
2nd year players +1.7
3rd year players +2.7
4th year players +3.2
Considering that the Buck's are getting older as a team and have few players that they have to gift playing time to, this might bode well for the team.
Another trend is that smallish all-star guards not named Curry really struggle in the play offs with plus/minus
Paul reg. season career p/m of +10.9, playoffs +7.1
Lillard reg. season career p/m of +7.0, playoffs -0.1
Kemba reg. season career p/m of +5.7, playoffs -5.4
Irving reg. season career p/m of +3.2, playoffs +0.7
Conley reg. season career p/m of +6.2, playoffs +11.1 (could be an exception)
Bledsoe reg. season carreer p/m of +3.4, playoffs last year of +1.4
Collison reg. season career p/m of -0.8, playoffs -9.2 (I know he is not an all-star, but is being replaced by a bigger guard in Brogdon)
Brogdon reg. season career p/m of +3.0, playoffs of -3.8 (remember Brogdon just finished his 3rd season so improvement is possible)
How about George Hill, career p/m of +3.9, playoffs of +12.0 in a 117 playoff games.
Hill is not flashy, but he gets stuff done and good things happen when he is on the court. And historically, when the pressure is on, he can take it to another level. Lets hope Father Time likes to winter in the south or SoCal (looking at you LeBron).
Just for fun here are the career reagular season plus/minuses of the Buck's rotation next year. Remember, 0 is the average and +6.5 was the median All-NBA players last year.
Giannis +5.2 (+9.7 last season)
Lopez +2.6 (+5.8 last year under Bud)
Robin Lopez +2.1
Brown -7.3 (had a +3.7 in the playoffs)
So going into next season the Buck's have 8 historically above average plus/minus players (not counting Donte because of sample size), 2 players with historically all-star level plus/minus, and one George Hill who might be the end of season piece that takes us over the top.