The first day of the Meijin match ended with the challenger's sealed move.
On the morning of the second day, the official opened the sealed move.
forbidden technique; prohibited move
Used for a maneuver or technique that is not allowed, especially in contexts such as sumo, martial arts, or competitive fighting. It overlaps in meaning with 禁じ手 but is a distinct use from the shogi/go sealed-move term.
Attacks aimed at the opponent's eyes are treated as a forbidden technique in this sport.
The player wrote down the sealed move and put it in an envelope.
The sumo wrestler used a forbidden technique and lost by disqualification.
The next day, the sealed move was opened and play resumed.
次の一手 simply means the next move to be played in a game, whereas 封じ手 refers to a move that has been written down and sealed for later, or to a forbidden technique.
Used to count moves (手) in games like shogi or go, as in 封じ手 "a sealed/reserved move".
A transparent compound of 封じ, from 封じる 'to seal, close off, prohibit,' and 手 'hand, move, technique.' In games it literally refers to a move that is sealed; the forbidden-technique sense reflects the idea of a move that has been closed off or prohibited.