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The Xs and Os of basketball: where it came from, how it is played now, the offense, and the defense that answers it

This site is for the person in the room who hears “they iced the drag and the low man tagged, so 5 short-rolled and hit the weak corner” and wants to know what happened. Every one of those words is defined here, in the place where it is used, with a picture.

How it is organized

Four chapters. Chapter 1 is where the game came from: the eras, each bounded by a dated rule change, and the players who defined them. Chapter 2 is how the game is played now, measured. Chapter 3 is the offense and Chapter 4 the defense, each in the order a possession happens, from the break to the late clock, and every offensive action names the coverage built to stop it. The table below is generated from the site’s own navigation, so it cannot disagree with the sidebar.

The sentence at the top of this page needs both Chapter 3 and Chapter 4: the drag and the short roll are offense, the ice, the tag and the low man are the defense’s answers, and the weak corner is court vocabulary, defined in Chapter 3 with the rest of the floor. Every one of those six words now resolves to a written lecture. If a lecture is ever a stub again, its entry in the table below and in the Reference says so, before the click.

Beside the four chapters, the Rules section compares eleven rules across five rule sets (NBA, NCAA men, NCAA women, FIBA, US high school), every cell cited to a rulebook on file or marked as a gap where the text is not public.

Chapters in reading order, from the sidebar.
Chapter Lectures
1. History and eras 1.1 Origins, 1891 to 1946 · 1.2 The Founding League, 1946 to 1954 · 1.3 The Shot-Clock Game, 1954 to 1979 · 1.4 The Three-Point Line, 1979 to 2001 · 1.5 The Paint Opens, 2001 to the Present
2. State of the game 2.1 What Is Different Now · 2.2 The Analytics That Drove It
3. Offense 3.1 Transition Offense · 3.2 Early Offense · 3.3 On-Ball Screens I: The Pick-and-Roll Family · 3.4 On-Ball Screens II: Named Ball-Screen Actions · 3.5 Off-Ball Screens I: The Screen Types · 3.6 Off-Ball Screens II: Named Off-Ball Actions · 3.7 Cuts, Seals, Handoffs and Post Play · 3.8 Sets and Systems · 3.9 Continuity and Read-Based Systems · 3.10 Spacing and Roles · 3.11 Motion, Conceptual Offense, Reads and Counters · 3.12 Special Situations, Offense · 3.13 Late Clock, Offense
4. Defense 4.1 Transition Defense · 4.2 Defending Early Offense · 4.3 Pick-and-Roll Coverages · 4.4 Help and Rotations · 4.5 Switching Schemes · 4.6 Zones and Junk Defenses · 4.7 Presses · 4.8 Special Situations, Defense · 4.9 Late Clock, Defense

The Offense and Defense pages list the same lectures by side. The Reference is the database behind the site: every term, one sentence each, with a link to the lecture that teaches it. The search box in the top bar reaches every entry.

How a lecture is written

Each lecture follows the same shape:

  • Under the title, a short block says which terms are new in this lecture and how many diagrams it has. That block is generated from the database, so it is never out of date with the entries.
  • Sections are numbered, figures are numbered and captioned, and the prose points at them: “see Section 3”, “Fig. 2”.
  • Each action or coverage is set out in a numbered card with the same slots every time. For an action: setup, trigger, read, payoff, beaten by. For a coverage: assignment, concedes, requires, beaten by. When a counter is introduced, its card shows what changed from the base action, the way a second model is shown as a diff of the first.
  • Every term is a link to its entry in the reference, and every entry links back to the lecture.

Reading a diagram

Offense is orange, defense is teal. A numbered circle is an attacker, the small filled dot beside one is the ball, and an X is a defender. A solid arrow is a cut or a run, a squiggle is a dribble, a dashed arrow is a pass, and a short thick bar is a screen; a teal arrow is a defender’s rotation. Diagrams are drawn to NBA dimensions from the rulebook, seen from above with the basket at the bottom; a press or a press break shows the whole floor with the far basket at the top.

What is a fact here and what is not

Definitions are terminology. They are written straight, because “a pin-down is a screen set facing the baseline” has no source to cite, only common use. Anything empirical carries a source: a number, a trend, a rule change, a claim that a team or a league does something more than it used to. If a claim of that kind has no source it does not appear, or it appears as a stated gap naming what is missing. That line is drawn on purpose, so that a definition can be trusted as vocabulary and a claim can be checked as a claim.

Status, generated 2026-09-27. 180 terms: 132 full, 6 partial, 42 short. Lectures written: 29 of 29 (1.1, 1.2, 1.3, 1.4, 1.5, 2.1, 2.2, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.11, 3.12, 3.13, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9).

Of the 42 short, 42 are vocabulary entries, which name a thing rather than an action and cap below full by design; none is an action missing its card. The 6 partial are tradeoff entries, which carry a why and no counter for the same reason. Every actionable entry on the site is full.

Stated gaps, by chapter: chapter 1 4, chapter 2 6, chapter 3 1, chapter 4 2. A gap is a claim this site could not source, named with the wall that stopped it.