When Azorius Arrester enters the battlefield, 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.)
4/15/2013 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.
4/15/2013 The static abilities of a detained permanent still apply. The triggered abilities of a detained permanent can still trigger.
4/15/2013 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.
4/15/2013 If a permanent’s activated ability is on the stack when that permanent is detained, the ability will be unaffected.
4/15/2013 If a noncreature permanent is detained and later turns into a creature, it won’t be able to attack or block.
4/15/2013 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.