At Competitive (Comp) and Professional (Pro) events the beginning of each match decks must be returned to their original state so they match their decklists. In other words, players must desideboard at the beginning of each match. Assuming that this is accidental, the proscribed penalty for failing to do so it a game loss. However if a player catches this error on himself when drawing his opening hand and calls a judge over, the head judge is allowed to fix the problem, have this player redraw their hand with one less card and downgrade the penalty to a warning.