# CORE ratings

Context & Opponent-Relative Efficiency (CORE) measures how much value a team
creates on offense and allows on defense after accounting for game situation
and opponent strength. It is designed to separate team performance from the
contexts and schedules in which that performance occurred.

CORE is an efficiency rating, not a forecast, point spread, or percentage.

## What goes into the rating

CORE uses qualifying pass and rush plays from completed FBS-versus-FBS games.
Each play is first compared with other plays that occurred in similar football
situations, including down, distance, field position, score, time remaining,
home-field context, and play type. The results are then adjusted across the
schedule so that offensive and defensive performance is evaluated relative to
the opponents faced.

The model excludes overtime, garbage time, FBS-versus-FCS games, special teams,
and non-scrimmage plays. Plays without the context required for a valid
comparison are also excluded.

This is intentionally a high-level description. CORE is a proprietary CFBD
model, so its fitted parameters and full calculation details are not published.

## Reading the values

- `offense` is points created above average per 100 qualifying offensive plays.
  Higher is better.
- `defense` is points allowed above average per 100 qualifying defensive plays.
  Lower is better.
- `overall` is offense minus defense. Higher is better.
- `offensePlays` and `defensePlays` show the samples behind the two components.
- `throughSeasonType` and `throughWeek` identify the inclusive endpoint of the
  snapshot.
- `modelVersion` identifies the methodology used for the stored result.

The API returns the stored calculation precision. Round values only for
display, and do not label them as percentages.

## Coverage and limitations

Public retrospective CORE ratings begin with the 2016 season. Historical
ratings are retrospective results from the released methodology rather than a
record of what the model would have reported at that point in time.

CORE describes team offense and defense over the qualifying plays in a stored
snapshot. It does not include special teams, player ratings, matchup
projections, spreads, or win probabilities. Early-season results also carry
more uncertainty because they are based on fewer plays and a less connected
schedule.

Use the [CORE ratings operation](/api/ratings#getcore) to filter by season,
team, or conference. A season or team is required.