At the beginning of your upkeep, detain target creature an opponent controls. (Until your next turn, that creature can't attack or block and its activated abilities can't be activated.)
Activated abilities include a colon and are written in the form “[cost]: [effect].” No one can activate any activated abilities, including mana abilities, of a detained permanent.
The static abilities of a detained permanent still apply. The triggered abilities of a detained permanent can still trigger.
If a creature is already attacking or blocking when it’s detained, it won’t be removed from combat. It will continue to attack or block.
If a permanent’s activated ability is on the stack when that permanent is detained, the ability will be unaffected.
If a noncreature permanent is detained and later turns into a creature, it won’t be able to attack or block.
When a player leaves a multiplayer game, any continuous effects with durations that last until that player’s next turn or until a specific point in that turn will last until that turn would have begun. They neither expire immediately nor last indefinitely.