Celtics’ double big experiment: is it working?

If you’ve been watching the Boston Celtics a lot this season – or reading CelticsBlog – you must have noticed that Joe Mazzulla and his coaching staff have increased their usage of the double big lineup concept. According to Cleaning The Glass, the Celtics have played 1,255 possessions with two big men on the floor and 2,622 with only one. Essentially, the Celtics spend about one-third of their time with two bigs.

When they play with one big, Al Horford has been the lone big man for 828 possessions, Luke Kornet for 680, Kristaps Porzingis for 588, and Neemias Queta for 526. The rotation is quite mixed due to injuries, rest needed for Horford, and varying matchups. The double big lineup also involves various combinations, but most of the time (985 possessions), Horford is the second big.

Why does it matter?

Now that we know the Celtics are alternating between double and single big lineups – and that most double big lineups feature Horford as the second big man – we need to examine the numbers to understand how each approach has worked this season. To assess the impact of these tactical decisions, we’ll analyze spacing, rim protection, and the possession battle. These are key aspects of modern basketball, and the number of big men on the floor directly influences all three.

More size theoretically improves rim protection because it allows for a big man to stay near the rim as a safety. Rebounding also tends to improve with size, helping win the possession battle. Additionally, size can crowd the paint and generate more turnovers.

However, more size can shrink spacing. It’s rare to have big men who are respected threats beyond the three-point line. Thus, the more big men on the floor, the trickier it becomes to maintain optimal spacing for driving lanes.

This was one reason Brad Stevens and his staff traded for Kristaps Porzingis last summer. With Porzingis or Horford as the lone big, the spacing is far better than with two bigs on the court. When Horford plays with Porzingis, defenses tend to leave Horford open from three, making his shooting more impactful when he’s the lone big man.

A single-big lineup also offers defensive flexibility. With Porzingis as the lone big, the Celtics can switch screens while keeping him close to the rim or play drop coverage in pick-and-roll situations. When Horford plays alongside wings and guards, he can switch on every screen or drop as well. With this context in mind, we’ll evaluate spacing, rim protection, and the possession battle for the different approaches.

Is the spacing really better with one big?

The screenshots above illustrate why double big lineups seem to create spacing issues. However, we need numbers to confirm this, because conclusions based on visuals alone can be misleading. To evaluate the Celtics’ spacing, we’ll examine rim frequency, efficiency, and the ability to draw fouls – essentially, how often and effectively the Celtics attack the rim.

The data quickly highlights that the Celtics’ spacing is best when Porzingis is the lone big. With him, the Celtics achieve their highest rim frequency, efficiency, and free-throw generation. Conversely, when Horford is the lone big, the Celtics lack rim pressure, with only 20% of shots within four feet of the basket and just 17 free throws made per 100 field goal attempts.

Double big lineups also show worse spacing compared to lineups with Porzingis alone. However, the numbers with Horford as the lone big and those with double bigs are quite similar. This can be attributed to two main factors. First, Horford is less respected as a shooter than Porzingis. Second, Porzingis’ positioning often maximizes spacing compared to Horford being in the corner most of the time.

Porzingis creates more spacing because he positions himself one pass away from a drive, while Horford is often stationed in the corner. A shooter in the corner provides less spacing than one positioned two steps beyond the arc on the wing or in the slot.

Horford’s floor spacing doesn’t vary much whether he’s a lone big or part of a double big lineup. Thus, it makes sense that spacing isn’t as strong with him compared to Porzingis. Offensively, we can conclude that double big lineups don’t optimize spacing compared to a lone Porzingis. However, spacing is similar whether Horford plays as a center or power forward. Now that we’ve analyzed rim attacks, let’s examine rim protection.

Is the double big lineup better at protecting the rim?

Defensively, the Celtics look very different depending on who plays center and how many bigs are on the floor. The aim is often to keep a big man near the rim or switch to prevent defensive gaps. It’s no surprise, then, that the numbers differ significantly depending on the approach.

With Porzingis as the lone big, the Celtics excel defensively, reducing opponents’ rim efficiency and attempts. On average, NBA teams take 32% of their shots at the rim at 66% efficiency, but with Porzingis anchoring the defense, the Celtics’ numbers are elite. In contrast, Horford’s lone big numbers explain why he’s often paired with another center this season.

As Horford ages, switch-heavy defenses become less effective. He struggles more against quick wings than before. While the Celtics use him in drop coverage, he lacks the length and instincts of elite drop bigs like Porzingis. Pairing him with another big helps offset these limitations.

Defensively, Porzingis as a lone big outperforms other approaches. Still, the double big lineup has its advantages in the possession battle.

The double big lineup generates more possessions

Despite its drawbacks, such as spacing and rim protection, the double big lineup has upsides. It excels at generating extra possessions.

Double big lineups are highly effective at offensive rebounding, ranking in the 86th percentile among lineups with over 100 possessions. Additionally, they secure more defensive rebounds and generate more turnovers, often leading to fast breaks.

Surprisingly, the Celtics are better in transition when they play bigger. By winning the possession battle, they create more transition opportunities despite the perceived limitations of size.

What to conclude?

Concerns about Porzingis’ lone big minutes and his negative net rating are overblown. The Celtics have simply experienced bad shooting luck when he’s on the floor. With opponents shooting 42% from three in these lineups compared to the Celtics’ 31%, regression to the mean will likely restore balance.

The double big lineup also has its strengths. It helps preserve Horford’s legs, wins possession battles, and provides depth. With Kornet and Queta exceeding expectations, a healthy Horford and Porzingis, and Tillman ready if needed, the Celtics have one of the deepest and most flexible big man rotations in the league.

When the playoffs arrive, this versatility will be invaluable in adapting to different matchups.