Rec League Scheduler — Fixtures, Rotation & Fairness for Volunteer Leagues

Overview

Volunteer-run rec leagues — badminton club, squash ladder, padel group, chess club, football 7s, curling, darts league — all die the same death: the schedule becomes a second job for one unpaid person, and the group chat becomes the database. Typical symptoms:

• "Who hasn't played each other yet?" — nobody knows.
• Two players have had 5 byes while others had zero, and there's a quiet mutiny.
• Absentees still occupy slots, so real attendance produces thin rounds and 3-court halls with 2 courts used.
• Standings live in a photo of a whiteboard from three weeks ago.

This skill is the volunteer's scheduling brain:

1. Fixture generation — round-robin (single/double) via the circle method; odd counts get a rotating bye; court/slot assignment included. Everyone plays everyone, in the minimum number of rounds.
2. Absence-aware rotation — mark who's absent on match day; the rotation re-flows so present players fill courts and byes fall to those with the fewest. Absences never consume playing time.
3. Fair-play audit — games played and byes per player, flagging any spread wider than ±1, plus pair-coverage (how many times each pair has met) so rivalries don't repeat while strangers never meet.
4. Availability registry — RSVP per date; call-up list for short rounds.
5. Standings — points, game difference, head-to-head tiebreaker, printed table.
6. Match-day sheet — one printable page: courts, slots, fixtures, score blanks, the byes, the next date.

When to Use

• You run a rec sports group of 4-32 players on a weekly (or multi-week) basis
• A club ladder or internal league needs a fair fixture list, not ad-hoc pairings
• Attendance varies week to week (5 one week, 11 the next) and rotation fairness is fraying
• You want standings that survive longer than a whiteboard photo
• Don't use for: knockout/tournament brackets with elimination (different structure — though fixtures seeds groups), leagues needing external governing-body rule compliance, or scheduling across many teams with venues/referees (that's full league-management software territory).

How It Works

1. player add "Alex" — build the roster (skill level 1-5 optional, used only for balanced court assignment notes).
2. fixtures --courts 3 --double — circle-method round-robin: each round lists courts and the bye; --double plays home-and-away.
3. absent "Sam" --date 2026-10-03 — registry of who's out when.
4. night --date 2026-10-03 --present 9 --courts 3 — tonight's actual rotation: present players re-flowed into courts, byes to the players with the fewest so far; prints the match-day sheet.
5. result "Alex" 21 15 "Sam" — record scores; standings builds the table (points, diff, head-to-head).
6. audit — the fairness report: games and byes per player (±1 target), pair coverage matrix summary.

Commands

# Roster
python3 scripts/league.py player add "Alex" --level 4
python3 scripts/league.py player add "Sam" --level 3
python3 scripts/league.py player add "Kim" --level 4
python3 scripts/league.py player add "Jo" --level 2
python3 scripts/league.py player add "Mel" --level 3

# Full season fixture list (5 players → bye each round)
python3 scripts/league.py fixtures --courts 2
# Round 1: [Alex vs Mel] court1, [Sam vs Kim] court2, bye: Jo ...

# Match night with real attendance
python3 scripts/league.py absent "Sam" --date 2026-10-03
python3 scripts/league.py night --date 2026-10-03 --present 4 --courts 2

# Results & standings
python3 scripts/league.py result "Alex" 21 15 "Mel"
python3 scripts/league.py result "Sam" 21 19 "Kim"
python3 scripts/league.py standings

# Fairness check
python3 scripts/league.py audit

State: league.json in cwd (or --db). Local, exportable, no accounts.

The Circle Method (what fixtures implements)

N players in a circle; fix player 1, rotate the rest; each rotation yields N/2 pairings (or (N-1)/2 + a bye when odd). After N-1 rotations every pair has met exactly once. It's the same construction used in professional league scheduling — minimal rounds, perfect coverage, zero repeats.

Fair-Play Rules (what audit enforces)

Common Pitfalls

1. Scheduling absent players. A fixture list is a plan, not a contract. night re-flows who actually came; byes go to the least-benched.
2. Odd counts without bye accounting. 9 players on 4 courts = 1 bye by arithmetic, not by choice. Unmanaged, the same nice person volunteers to sit every week. The rotation distributes it.
3. Letting standings drive pairings. "Top two should play" every week starves the bottom of the ladder and kills casual leagues. Fixture order is round-robin; standings are a report, not a scheduler.
4. Recording results from memory on Thursday. Score blanks on the match- day sheet exist because by Thursday nobody remembers 21-15 vs 21-18.
5. No shows → empty court, wasted hall fees. The call-up list (players who said "text me if short") fills rounds in seconds.
6. Skill-blind court assignment. Optional levels let you note "court 1 = the bloodbath, court 2 = the fun court" instead of discovering it by injured feelings in week 3.

Verification Checklist

• fixtures circle method: N-1 rounds (N even), N rounds (N odd), each pair exactly once (--double twice)
• Bye rotation spreads byes evenly; nobody bye'd twice in a row
• night excludes absent players, fills courts from present, assigns byes by fewest-byes
• standings sorts by points → game difference → head-to-head
• audit flags games/bye spread >1 and duplicate pair meetings
• Match-day sheet printable as plain text (one page)

References

• references/round-robin-math.md — circle method proof sketch, bye distribution for odd N, rotation re-flow algorithm, standings tiebreaker order