I'm not sure if I'm posting this Question in the right forum but. I was watching the 2010 WSOP on ESPN the other night and in one hand Davin Moon was in a hand with another player and by the time the River card was dealt Darvin had the nut flush and checked the River and got a hand Penalty. Now Darvin didn't know you have to bet the Nuts on the River. I know I'm still new to poker but when was that rule placed in tournaments? Also why is it a rule anyway? Shouldn't a player be able to play their hand the way they want to or is not betting the Nuts like Slowrolling someone even though Slowrolling is allowed in the game. Thanks in advance for the answer.