Quote from Comp. rules »
712.6. The controller of another player can’t make that player concede. A player may concede the game at any time, even if he or she is controlled by another player. See rule 104.3a.
Quote from UA livesOK, so if someone takes control of my turn and reaches for my sideboard can I scoop before he gets to have a peek?
Quote from UA livesI assume when I scoop the game ends immediately and he no longer controls my cards right?
104.3. There are several ways to lose the game.
104.3a A player can concede the game at any time. A player who concedes leaves the game immediately. He or she loses the game.