How to Defend at Gomoku: Block the Four, Deny the Double Threat

Gomoku looks like an attacking game, but the fastest way to raise your win rate is usually defense. As the mirror image of the attacking article (how to win), this is about spotting and erasing your opponent's threats before they land — in priority order. The whole of defense comes down to one idea: never let your opponent build a shape you cannot stop in a single move.

Top priority — always block a four

A four (one move from five) wins for your opponent next turn if you ignore it, so you must always block it. The flip side is that a four is forcing — it ties your opponent down too, since they must answer yours. When you block, don't just plug the hole: place the blocking stone where it also builds a three or four of your own, so you defend and attack at once (more below).

Don't ignore an open three — deny the open four

Reacting only once a four appears can be too late. If you leave an open three (a three with both ends free) alone, your opponent turns it into an open four next move — and an open four cannot be stopped: block one end and five forms on the other. So the key is to answer or break the threat at the three stage, not wait for the four. When the opponent's stones look ready to make a three in a row with room on both sides, deal with it early.

The heart of defense — deny two threats at once

A lone four or three can be stopped with a single block. What truly loses is a move that makes TWO unstoppable threats at the same time — a four-three (a four plus an open three in one move), a double-three (two open threes), or a double-four (two fours). You can only block one place, so the other one finishes. The essence of defense is therefore to occupy the key point where such a double threat would form, before your opponent does. As their stones spread, watch the squares where a four and a three, or two threes, could intersect.

Defend by attacking (offense and defense as one)

Pure defense eventually gets overrun. If you make your own four or open three, your opponent must stop and answer it — which interrupts their attack. A four of your own is especially useful: because it must be blocked, it buys you exactly one tempo. Train yourself to find the move that defends and creates your own threat in the same stone, and your defense and offense become a single line of play.

Renju defense (advanced)

In competitive Renju, only Black (the first player) has forbidden moves (double-three, double-four, and overline). That gives White a high-level defensive resource: steering Black toward a position where the only good continuation would be a forbidden shape. Free-style gomoku has no forbidden moves, and an overline (six or more in a row) generally counts as a win, so this idea is specific to Renju. Get a feel for fours, open fours, and double threats in free-style first; to compete more strictly, move on to Renju (and tsume Renju / VCF).

How to practice

Knowing the attacking shapes is the best defensive training there is. Solving TsumeDojo's tsume Renju (VCF) problems — winning by playing fours in a row — teaches you how fours connect into a win, which is exactly the same as knowing where to block to stop them. Once you can read an opponent's chain of fours in advance, your defensive accuracy rises too. Attack and defense are two sides of one coin: learn the attacking lines in VCF and put them to work on defense.