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NBA teams evaluate perimeter defense by combining matchup context, opponent shot outcomes, defender proximity and estimates of shot difficulty—not by treating one field-goal percentage as a complete verdict. Public NBA.com statistics show parts of that picture, but a closest-defender label is not the same as a possession-long assignment, and the league’s expected field-goal percentage (xFG%) is a shot model rather than a full rating of defensive decisions.
What perimeter-defense statistics are trying to measure
A useful evaluation separates three questions: whom a defender was responsible for, what shots the opponent took, and how difficult those attempts were. Those questions overlap, but no single public metric answers all three.
- Assignment and opportunity: Which opponent was matched with the defender, and what happened during those possessions?
- Contest and shot selection: How close was a defender when a shot went up, and from what location did the opponent shoot?
- Outcome and difficulty: Did the shot go in, and was its make probability higher or lower than expected for an average NBA player?
NBA.com’s public dashboards provide different views for these questions. The Teams Opponent Shooting: Closest Defender dashboard organizes opponent shots by the nearest defender at the attempt. The Teams Defense dashboard provides defensive measures, while the Teams Opponent Shooting dashboard reports opponent shot frequency and results. The NBA’s Stats Quick Links page connects to tracking, shooting and defense statistics.
How matchup data differs from closest-defender data
Matchup measures describe a pairing
The NBA glossary defines Deterrent Factor as the percentage of a player’s season-average field-goal-attempt output per possession that the player took in a specific matchup. Its formula is: (matchup FGA ÷ matchup possessions) ÷ (player’s season-average FGA per possession). In plain language, it compares an opponent’s shooting frequency against a particular defender with that opponent’s own season baseline. A lower figure may indicate that the player attempted shots less often in that matchup, but it does not by itself prove why: the pairing, team scheme, possession context and opportunities all matter. The NBA definition appears in its Stat Glossary.
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Closest defender describes proximity at the shot
Closest-defender statistics group attempts according to how near a defender was at the time of the shot, with a selectable distance range. This helps describe contest proximity and outcomes under different distance conditions. It does not establish that the nearest player was the primary defender throughout the possession. A switch, help rotation or late contest can mean the player closest at release was not the player who initially guarded the shooter.
That distinction matters when interpreting questions such as “How do matchup stats account for switches and help defense?” The public definitions distinguish matchup and proximity views, but do not document one universal process used by every NBA club to assign responsibility through switches, stunts and rotations. Team workflows and proprietary assignment data may differ.
What opponent shooting and DFG% tell you
The NBA’s team opponent-shooting dashboard reports opponent shot frequency, makes, attempts, field-goal percentage (FG%), effective field-goal percentage (eFG%), and separate two- and three-point results. Filters let users examine context such as season, shot range, game situation, team and date range. These splits help show both the shots a defense allowed and the results on those attempts.
Defended Field Goal Percentage (DFG%) is the opponent’s field-goal percentage on shots taken while a player is defending the shot; the calculation is defended field goals made divided by defended field goals attempted (DFGM/DFGA). That is an outcome measure, not a difficulty adjustment. A defender facing mostly contested long-range shots and one facing more attempts near the rim can have different DFG% results for reasons the raw percentage does not normalize. Read makes and attempts alongside shot location, shot type and frequency rather than treating DFG% as a standalone rating.
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What NBA xFG% adds—and what it leaves out
NBA.com defines expected field-goal percentage (xFG%) as “The field goal percentage that we would expect an average NBA player to shoot given the player tracking details of each shot taken.” It estimates the expected make rate for a shot using tracking information, helping distinguish a difficult attempt from a more ordinary one. It does not say whether the defender made the correct rotation, prevented a drive, forced a pass or successfully handled a difficult assignment.
How the NBA describes its tracking model
In an article published October 1, 2025, NBA.com Staff explained that the xFG% system uses optical player tracking and 3D pose detection. It tracks 29 points on each player’s body and generates 3D coordinates 60 times per second. For each attempt, the model examines the 60 frames—one second—before release. NBA.com says it uses separate models for jump shots and finishes around the rim, with inputs that include defensive contest posture, shooter orientation and balance, and court location. See NBA.com’s introduction to expected field-goal percentage.
Model boundaries
The published explanation says xFG% does not account for shot clock, shooter identity or score differential. The model is player-agnostic: it estimates shot probability under its stated inputs, not the full value of a defender or possession. NBA.com’s public methodology also does not establish that every NBA team uses this exact model internally.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical framework for comparing perimeter defenders
Use a sequence that keeps assignment, shot selection and shot results distinct:
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- Establish role and opportunity. Check which matchup is being measured, the number of matchup possessions and the opponent’s shot frequency in that pairing. Treat a matchup label as context, not proof of an unchanged assignment on every possession.
- Check proximity separately. Examine opponent attempts and results by closest-defender distance. Do not assume the nearest player at release was responsible for the entire possession.
- Compare shot mix. Look at attempts and frequency by location or range, including two- and three-point shots, before comparing outcomes.
- Put outcomes beside expected difficulty. Read DFG%, makes and attempts alongside xFG% when available. xFG% can provide a difficulty reference within the model’s stated scope; it is not a complete defensive grade.
- Check the sample and situation. Use available filters for games, minutes, opponent, season segment and game situation. A low opponent percentage on a small number of attempts may reflect shot variance or the particular shots encountered.
In reporting a result, state what the measure directly observed first—for example, opponent shooting percentage on shots with a defender within a selected distance—then explain the limits of what that observation establishes. Avoid turning one split into a definitive ranking.
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