Renju

Overview

Renju is a professional variant of the abstract strategy game Gomoku, played on a 15x15 gridded board (same as a Go board). Two players take turns placing black and white stones on the intersections of the grid lines. The objective is to get exactly 5 of your stones in an unbroken row (horizontally, vertically, or diagonally). Renju differs from Gomoku by imposing restrictions on Black (the first player) to compensate for Black’s inherent first-move advantage. These restrictions create a strategically deep and balanced competitive game.

Components

• 1 Board with 15x15 grid lines (225 intersections)
• Black stones (sufficient supply)
• White stones (sufficient supply)

Setup

1. Place the empty board between the two players.
2. One player takes Black, the other takes White.
3. Black always moves first.
4. Black’s first stone must be placed on the center intersection of the board.

Turn Structure

Players alternate turns:

1. Black’s Turn: Place one black stone on any empty intersection, subject to Black’s forbidden move restrictions.
2. White’s Turn: Place one white stone on any empty intersection (no restrictions).

Stones once placed are never moved or removed.

Actions

• Place a Stone: On your turn, place one stone of your color on any empty intersection (subject to restrictions for Black).
• Pass (optional): A player may choose to pass their turn. If both players pass consecutively, the game is a draw.

Scoring / Victory Conditions

• Win: A player wins by placing exactly 5 of their stones in an unbroken row (horizontal, vertical, or diagonal).
• Black’s Overline Rule: If Black creates a row of 6 or more stones, this does NOT count as a win for Black. Overlines are forbidden moves for Black.
• White’s Overline: White CAN win with 6 or more stones in a row.
• Draw: If the board is completely filled with no winner, or if both players pass consecutively, the game is a draw.

Special Rules & Edge Cases

Forbidden Moves (Black Only)

Black cannot play a stone that creates any of the following:

Forbidden Pattern	Description
3x3 Fork	Creating two simultaneous open threes (threes with both ends unblocked)
4x4 Fork	Creating two simultaneous fours (rows of 4 threatening to complete 5)
Overline	Creating 6 or more stones in a row

• 4x3 Fork (Legal): Black CAN create a fork with one four and one open three simultaneously. This is Black’s primary winning tactic.
• White has NO forbidden moves. White can freely create any pattern, including overlines.
• Forbidden Move = Loss: If Black plays a stone that creates a forbidden pattern, Black loses the game immediately.

Key Tactical Concepts

• Open Three: Three stones in a row with both ends unblocked, threatening to become an open four.
• Four: Four stones in a row with at least one end open, threatening to complete five on the next move.
• Open Four: Four stones in a row with both ends open; this is unstoppable (opponent can only block one end).
• VCF (Victory by Continuous Fours): A sequence of forcing moves using consecutive fours to create an unstoppable winning line.

Opening Rules (Tournament Play)

Tournament Renju uses specific opening rules to further balance the game:

• The first three moves may follow prescribed patterns.
• After the opening, the players may swap colors.
• Various opening protocols exist (Soosyrv, Taraguchi, etc.) to ensure fairness.

Player Reference

Concept	Black	White
First Move	Center of board (mandatory)	N/A
Win Condition	Exactly 5 in a row	5 or more in a row
3x3 Fork	FORBIDDEN	Allowed
4x4 Fork	FORBIDDEN	Allowed
Overline (6+)	FORBIDDEN	Allowed (can win)
4x3 Fork	ALLOWED (key tactic)	Allowed