Exposed cards?

[notdoinit]

A player in middle position raises.

Folds around to the blinds. The small blind thinks a while and folds. Big blind turns cards face up think he had just won because he didn't realize there was a raise.

Are the cards dead? Can he still play them if he wants to?

I quickly scanned the rule book and didn't see anything clear about this.

[holdemholmes]

The hand is not dead, but the player should be given a penalty/warning according to house rules.

[R-Ho]

The hand is not dead, but the player should be given a penalty/warning according to house rules.

Furthermore, if this happened in a cash game, heads up, it would be allowed without penalty.