The World Series of Poker Dealer Reference Guide 2010
SHOWDOWN:
If no players respond by revealing their cards when the dealer announces Showdown, the last aggressive bettor is required to show his hand first.
2010 WORLD SERIES OF POKER OFFICIAL TOURNAMENT RULES
Section VI- POKER RULES #63 At the end of the last round of betting , the player who made the last aggressive betting action in that betting round must show first. If there was no bet during the final round, the player to the left of the button shows first, and so on in clockwise direction. In stud games the player with the high board must show first. In razz, the lowest board shows first. At Showdown, any player at the table may request to see a folded hand from any player who has called all bets on the last round of betting. If a player with the last aggressive action on the last round jof betting refuses to show their hand and intentionally mucks his or her hand, the player in violation will receive a penalty, in accordance with rule #92.
2010 WORLD SERIES OF POKER OFFICIAL LIVE ACTION RULES
THE SHOWDOWN: 141. If everyone checks on the final betting round, the player who acted first is the first to show the hand. If there is wagering on the final betting round, the last player to take aggressive action by a bet or a raise is the first to show the hand. In order to speed up the game, the last player to act or a player holding a probable winner is encouraged to show the hand without delay. If there is a side pot, players involved in the side pot should show their hands before anyone who is all in for only the main pot. In a No Limit poker game if betting has ended on a round prior to the river, the player who pushed all-in is responsible for turning their hand over first.