Defense First: Block or Attack

Gomoku defense is the first thing a new player gets wrong and the hardest thing to correct. The default reaction is to block every three in a row, which leads to a passive game and a loss to a line that looked unrelated. The problem is not blocking too slowly. It is failing to tell which shapes demand an immediate answer, which can be ignored, and whether your blocking stone can also create a threat. This covers the decision rule and how to turn a defensive move into the start of a counter attack.

Not every three needs an answer

The only shape that demands a response is an open three. An open three is one move away from an open four, and an open four cannot be defended because both ends complete five.

• Are the three stones continuous, with no gap in the middle
• Are both ends empty, and does extending one space survive an immediate block

If one end is already blocked by your own stone or the board edge, that is a closed three. It produces a straight four with a single completion point, which you can calculate and handle later. Treating closed threes as open threes wastes a move.

Three shapes that demand an immediate move

In priority order. If any of these appears, your next move is largely decided.

• Open four: already lost. The real answer is to act before the opponent reaches this shape.
• Open three: must be blocked, but you can choose which end.
• Straight four: one completion point, so blocking that point is forced.

A straight four outranks an open three, because the next move completes five. If the opponent has both, take the straight four completion point first, then check whether the open three still stands.

Blocking your way to a loss

Following the opponent's shapes creates a fixed rhythm: they build a threat, you answer, they build another. You stay one move behind, because every move you make is decided by their previous one.

• Your stone placement is chosen by the opponent, so nothing accumulates around your own shape
• The opponent builds structure while threatening, getting two uses from one stone
• By the middle game, two or three threats exist at once and you can only answer one

To measure whether you are passive, count how many of your stones sit adjacent to the opponent's previous move. More than half means they hold the tempo.

Counter attacks: make the blocking stone a threat

A strong defensive move does two jobs. It blocks, and it builds your own shape. That is the gomoku blocking strategy worth learning, and it is what defensive play in gomoku is built around.

• When blocking an open three, pick the end that puts your stone on the extension of your own existing stones
• Prefer a position that creates a jump three or an open two over one that merely sits next to the opponent
• If the block also forms an open three, the opponent must answer you, and the tempo flips

The gain is not only efficiency. Once the opponent sees that every threat gets reversed into a threat against them, they have to spend moves defending, and the tempo comes back to you.

A check order you can run every turn

Scan the board in this order. It does not need long thinking.

• Check whether you have a five completion point. Take it.
• Check whether the opponent has one. Block it.
• Check whether you can form an open four in one move. Play it.
• Check whether the opponent can. Block the key point.
• Check whether you can form an open three that also blocks their open three. This is the best case.
• If none apply, play a stone that extends your shape in two directions at once.

Two of those six steps are about your own attack, which is the point. Offensive and defensive checks alternate rather than running defense first and attack later.

Three defensive misreads new players make

• Blocking a closed three as if it were open, spending a move for nothing
• Blocking the middle of a shape instead of an end, which does not remove the threat
• Watching only the opponent's most recent stone and missing an open two or three forming elsewhere

The third one is fatal. Continuous threats on the left pull your attention while the right side quietly reaches a winning structure.

The check order above only sticks if you repeat it in actual games. yiboardgame.com has an online play page with no signup required, and the in-browser AI keeps producing shapes that force these decisions. Rules are on the gomoku rules page, and the basics are in how to play.

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