How ratings work

Keiko League gives every athlete an Elo-style rating — the same idea used in chess and many competitive games. Your rating goes up when you beat someone and down when you lose, and the size of the change depends on how strong your opponent was. Beat a higher-rated opponent, gain more; lose to a lower-rated opponent, drop more.

A rating only ever changes from a confirmed roll — both partners have to agree the result. That keeps the numbers honest: every point on a leaderboard can be traced back to a result two people agreed on.

Elo calculation

Keiko League uses an Elo-style rating. Your rating changes only after both athletes submit matching results for the same QR session.

For each athlete:

• Expected score = 1 / (1 + 10 ^ ((opponent_rating - current_rating) / 400))
• Actual score = 1 for a win, 0 for a loss
• K-factor = 32
• Delta = round(K * (actual_score - expected_score))
• New rating = current_rating + delta

Quick example: if you beat a higher-rated athlete, your expected score is lower, so your rating gain is usually bigger. If you lose to a lower-rated athlete, your drop is usually bigger.

We also show rating reliability as rated-roll count beside Elo. Leaderboard rank additionally applies activity-based recency adjustments for inactive athletes.

Why only confirmed rolls count

Ratings are only useful if the results behind them are trusted. That is why one person cannot record a result alone: both partners report the same outcome, and the roll is recorded only when the two reports match. A disagreement, a cancelled session, or an expired session never changes a rating — and never spends a credit.

How rank reflects activity

A single good result should not put you top forever. Leaderboard position combines your rating with how recently you have competed, so a rank reflects consistent, recent training. Athletes who have not recorded a confirmed roll for a while appear under "inactive participants" with the date of their last roll.

How many rolls before a rating is reliable

A new rating starts at 1,000. Treat the first handful of rolls as a settling-in period: the more confirmed rolls you record, the more your rating reflects your real level. Look at the rated-roll count beside your Elo as a confidence label, not just your position on the board.

Source of truth: EloCalculator, RecordBout, and ConfirmQrSessionReport in the Rails app.