muck...

[markmagic]

after the flop SB goes all in and throw his card and he did not notice that UTG called...
some players says it is dead hand because he throw his hand in a forward motion
but some say that it must be show because it is all in...

[K-Lo]

Hi Mark:

If SB goes all-in and it is called by UTG, once all betting is complete, both hands must be shown.  It is not a dead hand simply because he attempted to fold, and the dealer should not muck the cards.  Assuming the cards are clearly retrievable and identifiable, the Dealer should return the cards to the SB and ask the SB to turn them over, since he is all-in and was called.  This is to protect other players in the tournament (e.g. otherwise, it would be too easy for the SB to 'dump' chips to his friend UTG).

TDA Rule 11: Face Up for All-Ins
All cards will be turned face up without delay once a player is all-in and all betting action by all other players in the hand is complete.

[ew2484]

Well said by k-lo, provided the cards aren't irretrievably mucked, the dealer needs to push back the cards and have the SB turn them over. This situation is also one of the very few where I will attempt to retrieve the cards when they have touched the muck, as long as they are clearly identifiable.