10. Invading a Sphere of Influence
How to Attack Weak Stones

by Richard Bozulich

It often happens that one side comes out of the opening with a large sphere of influence but little actual territory. There may be a thick wall on one side of the board and a corner enclosure on the opposite side, as in the example below, but the area between them is a no-man's land. One might argue that a corner enclosure surrounds territory, but that is not completely true. The territory it surrounds can disappear in a flash. It is better to regard a corner enclosure as simultaneously surrounding territory and projecting influence. Whichever it becomes depends on how the game develops.

If a player needs to establish a presence within a sphere of influence, he will be at a disadvantage and he must expect that his stones will come under attack. He has to find a way to quickly settle his stones. On the other hand, his opponent will try to use his influence to prevent the invader from accomplishing this.

Here is an example from a recent professional game that illustrates these points.

Highlight Diagram
Highlight Diagram
This position arose in a game in the 32nd Ryusei tournament between Yamashita Keigo 9-dan (black) and Kanazawa Hideo 8-dan. It was played on May 25, 2023.

Yamashita was one of the top players in the early 2000s. He won the Kisei title five times, and the Meijin and Honinbo titles twice each. One can get a feeling for the power and severity of his go in this example. His attacks are relentless and are made with pin-point accuracy. Just when you think White's group is safe, Yamashita goes after it in another direction.

Black has just played the marked stone, securing the territory on the left side. White must now find a way to establish a presence within Black's sphere of influence on the right side and prevent Black from turning this influence into territory.

Dia. 1. The conventional way
White 1 is the usual invasion point. No matter from which side Black extends, White will be able to make a stable two-space extension. Black will probably extend from his corner enclosure to 2, forcing White to make a two-space extension to 3 in the direction of Black's thick wall at the bottom. Still, White has established a presence, although a tenuous one, on the right side.

Dia. 2
Dia. 2. An alternative way
Black could also play a checking extension from below with 2. Again, White can make a two-space extension to 3. However, it is unlikely that Black would play at 2. Black's stones are overconcentrated and not working efficiently — the marked stone would be better placed at 'a'.

Figure 1 (1–5)
Figure 1 (1–5) Another strategy
In the game, White attached at 1. This is a tactic that is frequently used. It follows the principle "attach to settle your stones." Although it seems as if Black has strengthened his corner, there is still some bad aji there that White can exploit.

Instead of White 5 —

Dia. 3
Dia. 3. White has settled his stones
White usually thickens his position by pushing up with 5 and playing a hane at 7. He can now extend as far as 9.

Dia. 4
Dia. 4. Aji still remains
After White 9 in Dia. 3, Black aims to peep at 1. Black has no choice but to connect at 2. This peep would be especially effective if White had a stone around 'a'.

If Black resists —

Dia. 5
Dia. 5. Resistance fails.
Instead of connecting at 2 in Dia. 4, Black cannot resist by blocking with 2. White will atari with 3, then turn at 5. After White 7, it is clear that Black loses the capturing race and the corner as well.

Dia. 6
Dia. 6. Black's attack
The reason White didn't push up with 5 is that Black would attack with 6. This move is also an ideal extension from Black's wall below. White runs away with 7, but Black secures the top right with 8 and his bad aji in the corner has been eliminated.

Dia. 7
Dia. 7. White secures his stones.
White 5 in Dia. 3 is a move that Black would like to prevent, so pushing down with 1 may seem like a good move. White dodges with 2 and Black goes after the two white stones at the top with 3 and 5. In the process, White secures his stones with 4 and 6, so Black hasn't really gained much from this exchange.

Figure 2 (6–9)
Figure 2 (6–9). How the game continued
After White extended to the marked stone, Black attacked by pressing at 6. White defended with 7 and Black extended to 8. These were sharp moves by Yamashita. Again, White has to defend, and the diagonal move of 9 seems to be the safest move.

So why are Black 6 and 8 such good moves and what are they threatening?

Dia. 8
Dia. 8. Black takes profit.
After Black 1 (6 in Figure 2), White can't dodge to 2. Black will play a knight's move at 3. White defends with 4 and Black takes a big profit with 5. With Black's thick wall below looming over White's three stones, White will have to scramble to secure them.

Dia. 9
Dia. 9. White's stones are captured.
Black 8 in Figure 2 was also severe. If White tries to dodge by extending to 1 as in this diagram, Black will push in and cut with 2 and 4. White captures with 5 and 7, but Black captures a stone in a ladder with 8, so White's stones in the upper right are captured.

White 9 in Figure 2 eliminates this threat.

Figure 3 (10–16)
Figure 3 (10–16). An unrelenting attack
After White 9 in Figure 2, Black continued his attack on the white group with 10. Black 12 was the key point in this position; it made good shape and prepared for Black's final assault on White's group. White expanded his eye space with 13, then played the long-awaited peep at 15. Surprisingly, Black did not connect at 'a', but turned at 16. This was a brilliant move as it deprived White's group of two eyes.

What about the cut of White 'a'?

Dia. 10
Dia. 10. Not much of a threat
Unlike Dia. 5, Black can answer the peep by blocking at 1. If White 2, Black can connect at 3. Because of the marked stone, it is not so easy for White to break out into the center.

Dia. 11
Dia. 11. The game shifts to the top.
If Black timidly connected at 1, White could block at 2, so Black's attack on White's group would fizzle out. The game would now shift to the top with Black extending to 3.

Black 16 in Figure 3 puts on display Yamashita's unrelenting attitude, his fighting spirit, his refusal to let his opponent's weak group off the hook. Because of his thick wall below, he knows that he will prevail in this fight.

Figure 4 (17–20)
Figure 4 (17–20)
After White blocks with 17, Black can't put off connecting at 18 any longer. After White expands his territory at the top, Black plays the game-deciding move: the placement of Black 20.

White has no time to connect at 'a'. His group on the side would not have two eyes and Black could easily herd those stones towards his thick wall below and the game would be over.

Figure 5 (21–34)
Figure 5 (21–34)
With the moves to 31, White struggles to link up his stones to his allies on the left. However, it is all for nought. Black forces once with 32, securing some territory, then connects with 34, capturing four stones and taking a big lead.

One must be impressed at how skillfully Yamashita countered Kanazawa's invasion into his sphere of influence.

195 moves.
Black wins by resignation.

The move-by-move game record can be found at: Yamashita versus Kanazawa
Recommended reading
Identifying weak groups and knowing the techniques for attacking or defending them are essential for becoming a strong player. The explanations and problems in Attacking and Defending Weak Groups and 256 Opening and Middle Game Problems will teach you these techniques.