Events

Events are the discrete opportunities for what could happen with a given dice roll: whether you can hit, make or break an anchor, slot a point, etc. BackgammonDB analyzes the board position before the move, and then the board position after each candidate move, to produce a list of changes. It will tell you not just what you did, but what you could have — and should have — done.

Events are one axis of position tagging. For the structural labels see Position Types and Game Phases. For term definitions, see the Glossary.

Events

We group events into four categories: hits, anchors, slotting, and transitions.

Hits

Hitting can be defined as simply increasing the number of opponent checkers on the bar.

Event	Fires when
hit	You can put an opponent checker on the bar — the umbrella event for any hit.
double / triple / quadruple hit	You can hit exactly 2 / 3 / 4 opponent checkers (a triple or quadruple, of course, needs a double roll).
home-board hit	A hit can be landed in the mover's home board.
outfield hit	A hit can be landed in the outfield (the middle of the board).
deep hit	A hit can be landed in the opponent's home board.
point on blot	A hit can be landed where the mover also made the point on that spot (now two or more checkers there).
double tiger	The player can hit twice, both in the mover's home board, both left as blots.

The hit events stack. hit is the umbrella, and any move where any hit is possible gets tagged "hit." The three zones (home-board / outfield / deep) partition it — every hit falls into exactly one zone — and the count events (double / triple / quadruple) refine by how many were hit. So a double hit in your home board emits three events: hit, double-hit, and home-board-hit. And potentially double-tiger too!

Anchors

Anchor events are those when a point in the opponent's home board had zero or one checkers before, and now has two or more.

Event	Fires when
anchor made	A new anchor can be made.
anchor broken	A previously held anchor can be vacated.
made golden	The golden anchor — the opponent's 5-point — can be made (it goes from fewer than two checkers to two or more). This is the single most valuable anchor; it also counts as an anchor made.
back-split	The mover's back anchor on the opponent's ace-point can go from two checkers to one, the split checker staying deep.

Slotting

A slotting action is one where a point that had zero checkers can now have exactly one checker on it.

Event	Fires when
slot 5-point	The mover slotted their own 5-point (placed a single checker there from empty).
slot 7-point	The mover slotted their own bar point (the 7-point) from empty.
slot golden	The mover slotted the golden point — the opponent's 5-point (your 20-point) — from empty.

Making points

A point is made when it goes from fewer than two of your checkers to two or more — the opponent can no longer land there. We flag the two most important offensive points to make:

Event	Fires when
made 5-point	The mover can make their own 5-point — the best point on the board.
made 7-point	The mover can make their own bar point (the 7-point).

(Making the golden anchor — the opponent's 5-point — is its own event, made golden, listed under Anchors above.)

The midpoint

The midpoint is your 13-point, the long stack you start the game with. Giving it up is a meaningful structural decision, so we flag two flavors:

Event	Fires when
midpoint stripped	The midpoint drops from three or more checkers to exactly two — still held, but the spare builders are gone.
midpoint broken	The midpoint drops below two checkers — the point is given up entirely.

These two are mutually exclusive: a turn either strips the midpoint (leaving it made) or breaks it (giving it up).

Priming

A prime is a wall of consecutive made points that an opponent checker can't jump. We flag the moment a prime reaches a new length — but only when it is actually trapping an opponent checker behind it.

Event	Fires when
3-prime	A wall of 3 consecutive made points forms, trapping an opponent checker.
4-prime	The wall reaches 4 points, still trapping.
5-prime	The wall reaches 5 points.
6-prime	The wall reaches a full 6 points — an impassable prime.

Only the new longest length fires: a move that jumps straight from a 3-prime to a 5-prime emits 5-prime, not 4-prime. Six is the maximum — once you already hold a full 6-prime, extending it to a seventh consecutive point is not a new prime and fires nothing. (This event axis is separate from the six-prime position type, which labels the board as a whole — see Position Types.)

Transitions

These are broader state changes to the game position. Again, this codifies that the change can happen on this dice roll.

Event	Fires when
close-out completed	The mover can close the opponent out (the home board is filled and the opponent is on the bar).
race began	Contact was possible last turn but cannot be now — the game can become a pure race.
first bear-off	The player can take their first checker off this game.

The event verdict — played vs. best

This is what makes events powerful on the positions browser. For each event, BackgammonDB knows whether your played move did it, whether the best move does it, and whether it was possible at all — and that gives every event a verdict.

(Here, "you" and "your" are shorthand for "the active player." The first name in each row is the filter name used on the positions browser; the short name is the verb shown on the colored pill.)

Verdict	Short name	You did it	Best does it	You played best	Reads as
correctly did	did	✓	✓	✓	You did it, and it was the best move.
missed	missed	✗	✓	✗	The best move would have done it, and you didn't.
shouldn't have	wrong	✓	✗	✗	You did it, but the best move wouldn't have.
correctly avoided	avoided	✗	✗	✓	It was on the table; you and the best move both passed it up.
happened	—	✓	—	—	You did it, whatever you played — best or not.
possible	possible	—	—	—	Some analyzed move could have done it — the catch-all.

The You played best column is the one that's easy to miss: correctly did and correctly avoided both also require that your actual move was the engine's #1 play (zero equity lost).

Note that happened is a useful filter, which captures both "correctly did" and "shouldn't have" verdicts. But it is not a verdict shown on a pill; it will show either "did" or "wrong" depending on the verdict.

However, possible can show on an action. If no other verdict is chosen, it appears that you didn't do it, and it wasn't the best move. As a filter, however, it simply implies it was possible and makes no judgment on whether the action was taken.

A Note on "Best" and "Missed"

Keep in mind that the event verdicts simply compare the played move vs. the best move. It says nothing about the equity loss between the two moves. If your move is considered "Good" but not best — even if the equity difference is tiny — the event will be tagged as "missed."

Often, you will want to combine an event filter with the level of error. For example, "missed double hits" combined with "error level: error or worse." All event-related presets do this by default.

Future changes

BackgammonDB currently recognizes around thirty events, and this will grow in the future. The goal is to capture all key potential move types so we can better understand how we play backgammon and fix common mistakes. Whenever we make updates to the classifier, your position database will be reprocessed for you automatically. This may take a few seconds up to a minute or two depending on the size of your database.