Reversi Edge Strategy — Wedges, Stoner Traps, and Edge Control

Why Edges Matter

The four edges of the reversi board — row 1, row 8, column a, and column h — each contain 8 squares. Edges are strategically important for three reasons:

1. Stability potential. Edge discs connected to corners become stable — permanently locked for the rest of the game. A full stable edge represents 8 guaranteed points.

2. Corner access. Edge formations determine who gets corners. Wedges, unbalanced edges, and Stoner traps are all edge-based patterns that force corner concessions.

3. Endgame territory. In the late game, edges are some of the last squares to fill. How you play edges in the final 15 moves directly affects the endgame disc count.

But edges are also dangerous. Playing them too early expands your frontier, and overcommitting to one edge can backfire if your opponent exploits the formation. This guide covers when and how to approach edge play.

The Danger of Early Edge Play

In the opening and early midgame, avoid edge play whenever possible. Here’s why:

• Frontier expansion. An edge disc’s outer side is always adjacent to the board boundary and potentially empty squares — making it a frontier disc that gives your opponent outflanking opportunities.
• Premature commitment. Once you’re on an edge, you can’t easily change position. Central discs are flexible; edge discs are fixed in their strategic impact.
• Without corner support, edges are vulnerable. An edge full of your discs looks strong, but if your opponent takes the adjacent corner, they can flip the entire edge in one move.

When edge play becomes correct:

• After securing the adjacent corner (making edge discs stable)
• When a wedge opportunity exists
• In the late midgame when central moves are exhausted
• When gaining tempo through an edge play creates a strong positional advantage

Balanced vs Unbalanced Edges

Edge formations fall into two categories, and recognizing them is essential for edge strategy.

Balanced Edge

A balanced edge has discs from both players roughly evenly distributed, often alternating. Example on row 1:

_ B W B W B W _ (where B = Black, W = White, _ = empty corners)

Balanced edges are relatively stable (in the strategic sense, not the flip-immune sense). Neither player has an obvious exploit. The corners remain hard to force.

Unbalanced Edge

An unbalanced edge has one player dominating — typically 5 discs to 1 or 2. Example:

_ B B B B B W _ (5 Black, 1 White on the edge between two empty corners)

Unbalanced edges are tactically rich — usually to the disadvantage of the player with more edge discs. The player with fewer discs can often wedge into the formation or force a Stoner trap.

Why Unbalanced Edges Are Dangerous for the Owner

If you have 5 discs on an edge and your opponent has 1, your opponent has multiple potential wedge points and many ways to split your formation. Each split creates pressure on the adjacent corners. Having “more” edge territory actually makes you vulnerable.

Key principle: Having lots of edge discs without corner support is a liability, not an asset.

The Wedge

A wedge is one of the most powerful tactical tools in reversi. It occurs when you place a disc between two of your opponent’s discs on an edge, splitting their wall.

How Wedges Work

Imagine your opponent has a wall on row 8: _ W W W W W _ _

You place a Black disc between two of the White discs: _ W W B W W _ _

This splits their wall. Now their White discs on either side of your wedge can’t form a connected line. When they try to repair the damage — by playing adjacent squares to reconnect — they often:

1. Expose a C-square or X-square
2. Give you access to a corner
3. Worsen their position on the rest of the edge

When Wedges Are Available

A wedge opportunity exists when:

• Your opponent has a line of discs on an edge
• There’s an empty square between two of their edge discs (or between their edge discs and the corner)
• You have a disc behind the edge that creates a valid outflank for the wedge placement

Wedge opportunities often arise from earlier midgame play. A player who expanded to the edge too aggressively creates a long wall that’s vulnerable to splitting.

Playing Wedges Effectively

When you see a wedge opportunity:

1. Don’t rush it. A wedge opportunity often stays available for several moves. Play it at the moment that maximizes pressure.
2. Consider what it forces. The best wedges force the opponent to play on danger squares or give up a corner.
3. Check for counter-wedges. Before wedging, ensure your opponent can’t wedge you back on a different edge with worse consequences.

The Stoner Trap

The Stoner trap is the most famous edge tactic in reversi, named after competitive player John Stoner. It’s a specific unbalanced edge formation that forces the opponent to concede a corner.

The Setup

The classic Stoner trap looks like this on row 1:

_ B B B B B W _ (corners a1 and h1 are empty)

Black has 5 discs on the edge; White has 1 disc (at g1). The corner h1 is empty.

Why It’s a Trap

In this formation, Black can play h1 (the corner) by outflanking the single White disc at g1. But even if Black doesn’t immediately take the corner, the structure means:

• If White plays a1 (the other corner), Black takes h1 next
• If White plays elsewhere, Black can often take h1 at an advantageous moment
• White’s single disc at g1 is hemmed in and can’t expand without giving up something

The trap is that the 5-disc unbalanced edge gives the dominant player a guaranteed future corner — and the opponent can do very little to prevent it.

Variations

The Stoner trap has several variations depending on the exact disc count and positioning:

How to Avoid Being Trapped

The best defense against a Stoner trap is don’t let it form:

1. Don’t overextend on edges. Having 5 discs on one edge without corner support is the setup condition. Avoid creating it.
2. Wedge early. If your opponent is building an unbalanced edge, wedge into it before it reaches critical mass.
3. Avoid being the lone disc. If you’re the player with 1 disc on a 5–1 edge, you’re already in trouble. The formation should have been contested earlier.
4. Take the adjacent corner first. If you can secure the corner before the edge fills, the opponent’s edge discs become your converting targets rather than traps.

Edge Creeping

Edge creeping is a subtle technique of extending your presence along an edge one square at a time, using each play to gain tempo while your opponent is forced to respond.

How It Works

You have a disc on b1 (connected to your corner a1). You play c1, flipping a single opponent disc. Your opponent must deal with the new position. Next turn, you play d1. Each extension adds a stable disc to your edge wall.

Why Creeping Is Strong

1. Tempo. Each creep forces a response, giving you initiative.
2. Stability. Every new disc extends the stable chain from the corner.
3. Quiet progression. Creeping moves typically flip only 1–2 discs, keeping your mobility high.

When to Creep

Creeping is effective when:

• You own the anchoring corner
• Your opponent has discs along the edge to flip (enabling the outflank)
• You’re in the late midgame or early endgame when edge play is appropriate

Edge Strategy Principles Summary

Connecting Edge Strategy to the Full Game

Edge play doesn’t exist in isolation. It connects to every other strategic concept:

• Corner strategy — edges are the path to corners and the payoff from corners
• Stable discs — corner-anchored edge discs are the primary source of stability
• Mobility — early edge play kills mobility; late edge play converts position into territory
• Endgame — edge squares are often the last to fill, making edge control critical for the final sequence
• Openings — opening choices affect which edges become contested in the midgame

The best reversi players don’t think about edges as a separate topic — they see edges as one part of an interconnected positional landscape where corners, mobility, and stability all flow together.