Numbers Game: Understanding Opponent Strength

One important consideration in fantasy is the strength – or lack thereof – of a player's opponent. Late last season, if I was struggling with which of two players to start, seeing that one's opponent was the Lakers or 76ers (or, failing that, the Kings) made for an easy tiebreaker. Playing one of those teams was like injecting your lineup with steroids.

At the beginning of the season, however, I'm typically hesitant about targeting one opponent or another. Will the addition of Player X or Coach Y make a difference? So-and-so gained 20 pounds of muscle – will that help them defend the lane? The modern NBA sees more offseason shifts than ever.

Even after the first several games, I question whether the early data is reflective of the team, or their schedule. Five of the Knicks' first seven games are against teams that ranked in the bottom half of the league for pace last season. If the Knicks' early pace numbers are low, is that a result of the Knicks, or who they played?

With all this in mind, I went looking for answers. My task – discover whether last season's team defensive metrics are meaningful for predicting this year's results.

I am focusing this column on my three favorite defensive metrics: defensive rating, or opponent points per 100 possessions; rebound percentage, which is the percent of available rebounds one team grabbed; and pace, the number of possessions a team averages during 48 minutes.

Methodology

I looked back through the last four years of data – every full season since the strike-shortened, and therefore schedule-altered, season of 2011-12. Within each of the three metrics, I ran an analysis to see what the relationship was between a team's relative performance from one year to the next. For example, first I checked the relationship between any team's relative performance in defensive rating from 2012-13 to the same in 2013-14; then I ran the same test, starting fresh, checking the relationship between any team's relative performance in defensive rating from 2013-14 to 2014-15, etc.

More important than the relationship, however, is the strength of that relationship. I don't need to use math to predict that a strong defense or fast-paced team one year is more likely to be a strong defense or fast-paced team the next. I, therefore, checked the strength of the correlation for every data set compared.

Defensive Rating

Defensive rating is the advanced metric I use most when assessing fantasy opponents. Unfortunately for our purposes, however, there was not a strong relationship between a team's defensive rating from one year to the next. That said, there are still some takeaways we can use.

The general trend from one year to the next is movement toward the league average. As can often be true of math and statistics, this trend reflects our logical assumptions. The worst teams one year are likely to improve, and the best are likely to get worse. As stated above, the relationship was not a strong one, but the overall pattern was clear.

Most of the fantasy impact of opposing defenses comes at the extremes – the very good, and the very bad. Among those groups, two clear trends emerged:

• The very bad teams don't stay very bad. During the four seasons I analyzed, only three teams placed in the worst 20 percent of the league during consecutive seasons: the 2012-14 Hornets, the 2014-16 Timberwolves and the 2013-16 Lakers, the only team to three-peat as league bottom-feeders. This is particularly useful information for daily gamers – early in the season, teams facing the Lakers, 76ers and Kings will have their salaries raised because of their "easier" opponents, but the price increase is likely disproportionate to the actual weakness of the opponent.

• The very good teams have done a better job of staying very good. Three of the four best defenses in 2012-13 remained among the five best in 2013-14. Two teams each, the Spurs and the Warriors, remained in the top 5 throughout 2013-14, 2014-15 and 2015-16.

• The Spurs have remained a top-5 defense throughout all four seasons of the sample. Always avoid players playing the Spurs if you have the choice.

Rebound Percentage

The results here were far more disappointing than the results of the defensive rating analysis. My goal with this column is to provide actionable information to improve fantasy teams. In this category, however, the best I can offer is to ignore the previous season rebound percentage data.

For two years of the data, the relationship was very weak. For the third year, the relationship was scarcely better than flipping a coin.

While the league-wide trend was not much better than meaningless, three teams showed remarkable consistency throughout my data set. The Hawks and the 76ers were among the bottom 20 percent all four years, while the Thunder remained in the top 20 percent. Unfortunately, all three teams went through significant offseason changes. As result, even for those three teams, it seems unwise to assume that their recent performance will continue.

Pace

Finally, some good news. A team's pace in one season has some predictive value for projecting its pace in the following season. Considering the dynamic nature of the league, and the amount of shifting variables, the relationship is about as strong as I was hoping for.

Generally speaking, fast teams stay fast, and slow teams stay slow. For most teams, their pace relative to the rest of the league stays similar from one year to the next. Three teams ranked in the fastest 25 percent of the league throughout all four seasons of my sample; four teams ranked in the slowest 25 percent of the league throughout all four seasons. Six teams ranked in either the top or bottom 20 percent for three seasons in a row. That kind of sustained extreme behavior is great for fantasy managers – not only is last year's data worth considering, but we do not have to assume that the fastest and slowest teams will move significantly toward league average.

Each season, a handful of teams experienced significant shifts in their pace compared to the rest of the league. A little less than half of those changes correspond with coaching changes, such as the Warrior's increasing their pace in the 2014-15 season. The following teams have new coaches this season: Grizzlies, Kings, Knicks, Lakers, Magic, Nets, Pacers, Rockets, Suns, Timberwolves, Wizards.

Conclusions

Analyzing fantasy opponents based on the previous season's advanced metrics comes with some serious pitfalls, but it has some value. The most useful information is pace, where most teams stay pretty similar from year to year – very fast teams tend to stay very fast, fast teams tend to stay fast, etc.

When it comes to defensive rating, there is meaningful movement from year to year, so take last season's data with a grain of salt. Don't be too easily seduced by seeing last year's worst teams – it may still be bad, but it has probably improved. Also, avoid the Spurs. Gregg Popovich is king.

As for rebound percentage, last year's data is probably not worth paying attention to.