This is a setup called the "Hook," named for the way the piece hooks in. It is performed on what is known as a "Dead Shape," or a shape that is normally difficult to clear. Using a "J" and a "Z," one can clear the obstacle. In games that reward All-Spins, this is powerful knowledge. One can also intentionally create it, allowing for All-Spin reward.
Basic Shape
Variant
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J-Spin Double
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Z-Spin Double
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Empty Field Setup
Continuation
T-Spin Triple
Possible alternative whenever a T-Spin Triple setup is present.
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J-Spin Double
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Z-Spin Double
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Captain Hook
One can open with a TST, leaving a Hook behind (JSD into ZSD).