“Trap The Box”

Term: Trap the Box

Definition: A technique in which the low and weak-side help defender rotates to the strong-side block to defend a slot, wing or corner drive.

Synonyms: N/A

Explanation: Before defining “trap the box,” we must widen the lens to discuss a larger question: What is “help defense?” Although this term is often thrown around imprecisely, it actually encompasses a very prescribed set of movements that govern NBA defenses. Given the randomness of each individual basketball play, it is impossible for defenses to plan for every potential offensive scenario. Instead, most NBA coaches use a similar set of principles that deal with the most common forms of offense.

Although the pick-and-roll is the bread-and-butter action of the NBA, one-on-one play is the foundation upon which defenses are built. There is no need for a ball-screen if a defender can’t guard his man — an important truth in today’s era of supremely skilled offensive players. To counter this natural advantage, NBA defenses have designed an entire helping scheme to minimize the damage. While there are some natural cracks — after all, the concept of help logically involves leaving someone open — it is remarkably efficient when executed properly.

At the heart of NBA defensive strategy is the “no middle” concept, which dictates that the ball be kept out of the middle at all costs. The reasoning behind this is straightforward: If an offensive player gets into the paint, he has the entire floor at his fingertips. If an offensive player drives baseline, he’s limited both by the baseline out-of-bounds line and his distance from the weak side. Fewer options equals fewer places to guard.

“No middle,” however, does not give on-ball defenders carte blanche to swing the gate open to the baseline side. Defenders are still responsible for staying in front. But if penetration does happen, it should not slice through the heart of the defense.

Offensive players are further discouraged from driving middle by the placement of help on the “nail” — the spot right in the middle of the free-throw line. That’s what Ricky Rubio of the Minnesota Timberwolves is doing here as the ball is guided baseline by teammate Karl-Anthony Towns. NBA defenders generally do not deny one pass away — they sag to protect the middle. Rubio is several feet away from his man, Will Barton of the Denver Nuggets, for that exact reason. Should the ball get swung to him, Rubio will return to a guarding position on the ball.

How To Trap The Box

We’ll take the no-middle concept as a given in the exploration of trapping the box, because without it, organized help principles disintegrate. Trapping the box, then, is the first layer of help defense when an on-ball defender gets beaten to the baseline side. But which player offers that help? Somewhat counterintuitively, it’s not anyone near the ball: It’s the low and weak-side defender — preferably a big — who is usually guarding an offensive player in the opposite corner or the weak-side dunker spot.

(Note: The trap-the-box man is on the strong side if his man sits in the strong-side dunker. However, offensive bigs rarely sit in the strong-side dunker because they would clog up the driving lane.)

As it happens, this is usually the player who is two-nining — he has the luxury to venture away from his man because of his distance from the basketball. If he is doing his job properly, he is already stationed near the middle of the paint when the drive occurs. It is only a short distance, then, for him to step up into a primary and on-ball help position.

Most commonly, drives occur from one of six spots: The corners, the wings, and the slots (The “slot” is the spot where the three-point line and the line marking the outer edge of the paint would theoretically intersect.) As the offensive player readies his attack, the defense prepares itself for a set of instantaneous strong-side movements.

(Note: Only strong-side defense will be covered in this post. The backside rotations will be covered in follow-up posts.)

  1. If beaten, the on-ball defender maintains inside positioning as much as posssible.
  2. If the strong-side corner is filled, the strong-side corner defender stunts at the driver without abandoning the corner shooter.
  3. The weak side low man shifts from two-nining to trapping the box — meaning he becomes the primary help defender by greeting the driver in his path.

Below is an example of all three facets in play, as Yogi Ferrell of the Dallas Mavericks isolates against LaMarcus Aldridge of the San Antonio Spurs.

Aldridge, recognizing that he is the much slower player, backs up a few steps. But his positioning dictates more than that. Keeping our no-middle concept in mind, on-ball defenders typically try to keep the ball on the same side of the floor as it starts. Better defenders, therefore, keep their inside foot slightly higher to encourage a baseline drive. Here, we can see Aldridge doing just that as he keeps his inside (left) foot higher up the floor. While his positioning is a bit exaggerated to compensate for the mismatch, it is nonetheless conceptually sound.

Once Ferrell darts left, Tony Parker must stay put on Seth Curry in the corner. While Parker might appear to occupy a natural help position, Ferrell would only need a quick pitch to hit Curry for an open corner three — the easiest long-range shot. There simply is not enough time for Parker to stick his body in front of Ferrell, pivot, and sprint back to Curry. That’s why the rule here is a quick stab at the ball, at most. Abandoning the strong-side corner is a recipe for enraging any coach.

Danny Green on the weak-side elbow is not a trap-the-box candidate due to his angle of pursuit: He is too perpendicular to Ferrell’s potential driving path and could not cut it off. Kawhi Leonard could do the job, but there’s a bigger, more logical option who is already two-nining: Davis Bertans.

Notice how Bertans’ orientation aligns him with the ball. He can step up legally into Ferrell’s potential path with the least amount of risk. His eyes are trained on the mismatch, and he is already in the process of clearing to the weak side (to reset his 2.9 clock) before Ferrell drives. He does not want to get caught sliding away from the ball when Ferrell bursts forward, so he preemptively buys himself more time in the paint.

As Ferrell approaches the key, all of the pieces fall into place. Aldridge funnels Ferrell left. Parker stays attached to the corner; Bertans traps the box early and protects the rim.

Essentially double-teamed, Ferrell has his shot blocked by picture-perfect verticality. This freeze-frame, however, also captures why NBA coaches want Bertans — the low and weak-side defender — to trap the box: Despite two players being thrown at Ferrell, he has nowhere to go with the ball. Ferrell’s only options are Harrison Barnes on the weak-side block (Kawhi Leonard should really have a more inside position here, but we’ll let that slide for now), and Dirk Nowitzki in the opposite corner. Given the intense ball pressure created by trapping the box, the passing lanes are thin — that’s why leaving Dirk open momentarily is fine. Few players can thread the ball through such tight spaces.

Early diagnosis is crucial. Help defense is about mental activity — keeping your head on a swivel and preparing for potential dangers. It’s easy to slide in and out of the paint as the two-nine defender, but timing up trap-the-box movements requires foresight.

When these rotations are missed — namely trap the box rotations — they fly under the radar. As a secondary defensive maneuver, it’s easy to miss. But accepting the premise that on-ball defense is a multi-person endeavor allows blame (and praise) to be awarded properly.

Take a look at the play below involving Devin Booker of the Phoenix Suns, who beats Jerami Grant of the Oklahoma City Thunder left. Enes Kanter, who is trying to communicate a switch with teammate Semaj Christon (Derrick Jones Jr. of Phoenix mucks things up with a flare screen for Alex Len in the corner), loses track of the ball. With his eyes peeled on the weak side, he’s not ready for his primary help responsibility. The play is essentially over before it begins.

Before the Booker isolation takes shape, Kanter has time to negotiate the switch. But his inability to capitalize on this brief pause leaves him handling two responsibilities at once. The result is him missing his trap-the-box rotation, and Booker scores. Grant, left on a defensive island, looks guilty.

If defense has one essential tenet, it’s this: Stop the ball. Most players can’t do it by themselves, so teams adjust to account for this reality. Trapping the box is the first rotation domino. As far as isolation help defense goes, all else fails without it. The verticality, the prevention of kick-out threes and all the rest are important. But giving up dunks and layups renders everything else moot.

When we think of rim-protectors, we think of bigs blocking shots or going vertical. But the real work involves all five players knowing every defensive spot. Especially with the interchangeability of positions in today’s NBA, wearing multiple defensive hats is a must. Anyone can become the low man at any time. That’s why everyone must know how and when to trap the box.


Film Study: “Trap the Box”

Below is a video compilation of various examples of defenders trapping the box. As you watch the film, take note of where the help comes from: Whether it’s a big or a wing, whoever is in that low and weak-side position shoulders the primary help responsibilties. There are back-side obligations here too, but keep your focus on the strong side for now.

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