Oshitsubushi
is oshi-tsubushi, literally "squashing push", a Japanese term (also used in English) for a life and death tesuji. The everyday translations, crush, squash, and smash, are also occasionally seen.
After , White's connection at the marked point is an illegal suicide move under most rulesets. Later Black can capture the two White stones, gaining two eyes and life.
If White to play, she can kill Black by connecting at and forming nakade. If
captures the three stones, White 3 at
holds Black to one eye.
If Black misses the oshi-tsubushi and instead takes the ko with , White plays under at
and Black will die. Taking with
is useless; White throws in with 4 at
and Black only has a false eye here. (If instead of
White mistakenly treats this as a ko fight, making a ko threat and then retaking the ko, Black gets a second chance at oshi-tsubushi.)
Under rulesets which allow self-capture, is possible; the three White stones are then immediately removed. However,
now kills White. Because Black must respond, however, the self-capturing move can be used as a ko threat.
Oshi-tsubushi can be prevented by damezumari. In this position, Black's lack of liberties means that with he is putting himself into atari.
Black lives with the sacrifice and oshi-tsubushi at
.
White should have recognised that this is a bent four in the corner position and played at herself.
See also: