Seed Withdrawal Cascade

Overview

When a seeded player withdraws from a tournament after the draw has been made but before play begins, governing bodies (ITF, ATP, WTA, USTA) require a cascade: one seed from each lower seed block moves up to fill the vacancy, preserving proper seed distribution throughout the draw.

The Competition Factory implements this as the seedWithdrawalCascade mutation, available as a position action (SEED_CASCADE) when clicking on a seeded participant's draw position.

Seed Blocks

Seeds are organized into blocks that correspond to their placement in the draw:

Block	Seeds	Draw Position Purpose
1	1	Top of draw
2	2	Bottom of draw
3	3–4	Semi-final quarter separation
4	5–8	Quarter-final separation
5	9–16	Round of 16 separation
6	17–32	Round of 32 separation

The number of populated seed blocks depends on the draw size and seeding policy:

Draw Size	Max Seeds (Default Policy)	Blocks
4	2	[1], [2]
16	4	[1], [2], [3-4]
32	8	[1], [2], [3-4], [5-8]
64	16	[1], [2], [3-4], [5-8], [9-16]

How the Cascade Works

When a seed withdraws, one seed from each successive lower block moves up to fill the vacancy. The cascade stops at the lowest populated block, leaving a single vacancy for the tournament director to fill.

Example: Seed 3 Withdraws (64-draw, 16 seeds)

Seed 3 (block [3,4]) withdraws
  → Seed 5 (block [5-8]) moves into Seed 3's draw position
    → Seed 9 (block [9-16]) moves into Seed 5's draw position
      → Vacancy at Seed 9's original draw position

The tournament director then fills the vacancy at Seed 9's old draw position with an alternate or assigns a BYE.

Example: Seed 1 Withdraws (16-draw, 4 seeds)

Seed 1 (block [1]) withdraws
  → Seed 2 (block [2]) moves into Seed 1's draw position
    → Seed 3 (block [3,4]) moves into Seed 2's draw position
      → Vacancy at Seed 3's original draw position

Key Rules

• One replacement per block: Only the lowest-numbered seed from each lower block moves up — not all seeds shift.
• Seed assignments update: When Seed 5 moves to Seed 3's position, Seed 5's participant occupies seed slot 3 in the seed assignments.
• The vacated position is wherever the last moved participant was originally placed. This can be anywhere in the draw since seed placement follows block patterns.
• No cascade from lowest block: If a seed in the lowest populated block withdraws, there is no cascade — only a vacancy at that position.

Usage

As a Position Action

The SEED_CASCADE action appears in positionActions when:

1. The draw position contains a seeded participant
2. The structure is MAIN stage, sequence 1 (not consolation or playoff)
3. The structure is not round robin
4. No matchUps have been played (pre-tournament only)
5. At least one lower seed block has assigned seeds

const { validActions } = tournamentEngine.positionActions({
  drawId,
  structureId,
  drawPosition: seedDrawPosition,
});

const cascadeAction = validActions.find(a => a.type === 'SEED_CASCADE');
// cascadeAction = {
//   type: 'SEED_CASCADE',
//   method: 'seedWithdrawalCascade',
//   payload: { drawId, structureId, drawPosition }
// }

Direct Mutation

const result = tournamentEngine.seedWithdrawalCascade({
  drawId,
  structureId,
  drawPosition: withdrawnSeedDrawPosition,
});

// result = {
//   success: true,
//   vacatedDrawPosition: 13  // where the TD needs to fill
// }

After the Cascade

The vacatedDrawPosition in the result tells the tournament director which position needs to be filled. They can:

• Assign an alternate using the standard alternateDrawPositionAssignment action
• Assign a BYE using the assignDrawPositionBye action
• Assign a lucky loser if applicable

Timing Constraints

Per ITF/ATP/WTA regulations:

• Before order of play released: Full cascade applies — seeds move into higher seed positions
• After order of play released: No cascade — the vacancy is filled directly by an alternate or lucky loser using the standard withdrawParticipantAtDrawPosition action

The seedWithdrawalCascade mutation enforces the pre-play constraint by checking that no matchUps have active draw positions.

Governing Body References

• ITF: "Any vacancy created by the withdrawal of a seed shall be filled by the next highest ranked player eligible to be seeded"
• ATP/WTA: Next eligible player takes the withdrawing seed's position; the remaining vacancy is filled by an alternate/lucky loser
• USTA: Seed replacement follows the same cascade principle with policy-defined seed count thresholds