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On Volatility

The Houston Rockets average 107.1 points per 100 possessions, a number that’s good for fifth in the league. The Denver Nuggets sit at third with 107.5, and the San Antonio Spurs are just a touch behind them with 107.3. The Rockets are undoubtedly one of the most proficient teams in the league right now. Yet in the last two games the Rockets put up first half scores below 40. In fact, the Rockets’ totals against the Golden State Warriors alone have run the gamut from 140 points in regulation to a paltry 78. How can one team exhibit such inconsistency?

The Rockets have been called inconsistent all season, and that’s an accurate take. Their margin, while good on the year (+3.18 points per game on the year, good for 8th in the league), would tend to suggest a higher win total. In fact, the Rockets seldom actually win games by a few points, tending instead to offset blowout wins with ugly losses. They don’t play much better against bad teams than against good teams, and even with the dreadful loss to the Warriors are still looking better after the All-Star break than before it. They’re simply a team that’s wildly unpredictable from one minute to the next, scoring 39 points in a half before scoring 69 in the second half of the very same game.

The explanation is, in a word, volatility. This volatility is a systemic issue, and while maturity, cohesion and chemistry may improve the issue, the way Houston plays the game is simply going to cause these swings to occur. The volatility of scoring within one game is the easiest to see. They Rockets use the most possessions per game (a blistering 98.8), giving both teams more chances to score, miss, turn the ball over, etc. “Streakiness” can easily be understood as simply a function of probability. As most players in the league shoot less than 50% from the field, it’s no more surprising for five shots to miss in a row than it is for five coin flips out of a hundred to be heads all in a row. The more possessions there are, the more chances there are for streaks to form.

Of course, basketball players and coaches are people and not dice, and their ability, mentality and health play the largest roles in the dice rolls. The point here is simply that using many possessions increases the likelihood of volatility within a single game by providing more chances, not that it guarantees it. The paradox here is that these high possession games actually decrease volatility overall, as more chances to roll the dice allow more chances for regression to the mean. If a team shoots 45%, the more shots they take, the closer to that number they are expected to get. So why, then, do the Rockets see such variance?

They shoot threes, and they shoot free throws. These are the most efficient shots in basketball, but by coincidence they also have inherent problems with volatility. The three pointer’s case is obvious. As it’s worth a full 50% more points than a three, you can accept a massive drop in accuracy and still come out ahead in the long term. It’s no secret that the Rockets try to avoid midrange shots, and that’s exactly why. The only problem here is that as your accuracy decreases, so does the chance of spikes and troughs.

Quality of looks aside, the Rockets shoot well from deep (37.2%, 6th in the NBA), and they purposefully take a lot of them (a league-leading 29.1 per game). This isn’t new information, and I’ve talked about it before, but it informs a lot of what happens to Houston. they can expect about 32 points a game from threes, but given that this comes from only 29 tries, it’s actually normal for this to skew a lot, leading to huge wins or ugly losses.

Free throws only compound this. While each attempt is at a much higher percentage (around 77% on average), and consequently should be more stable. In fact, though not above average in accuracy, Houston is one of the two most prolific free throw shooting teams at 25.3 attempts per contest. No small part of this is due to James Harden’s league-leading 10.1 per game. Given that they should be getting a rather consistent 19 points per game from these, where does volatility come in?

The fact of the matter is that free throws are dependant upon a variety of factors outside of Houston’s control. Not only can different defensive schemes limit or promote fouls inside, but the nature of the foul call itself makes is hard to rely upon free throws from quarter to quarter. Refereeing NBA basketball is incredibly difficult, and it’s unreasonable to expect NBA referees to be able to perfectly judge everything. Refs will tend to err one way or another, and this isn’t a problem so much as a necessity. Some days contact on the drive is verboten and some days Harden leads a parade in red to the charity stripe. Some days the Rockets simply aren’t aggressive getting to the rack when someone like Bogut is handing down defensive punishment. For many reasons, free throws tend to come in spurts, just like threes.

The Rockets’ lack of stability isn’t anyone’s fault. In fact, it isn’t even necessarily a problem. Many teams, like the Celtics and Sixers, prefer to stand by the steady, predictable two point shot. Like any strategy, this can work, especially in a strong defensive system. But with Houston’s emphasis on speed, efficiency and gunning, this is largely a part of their team identity. The same factors that give Houston historic blowouts against the Warriors are the factors that give Houston season-worst performances to that very same team.

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