A valid 8 low hand contains 5 cards of unique rank 8 or lower (no pairs). The ace is considered a low card. When comparing valid 8 low hands the hand with the lowest high card takes precendence. If this is the same then the next lowest card in each hand is compared. Suits are ignored.
8 low is always played as part of a split pot game. If no player has a valid 8 low hand, the entire pot will go to the best hand of the other ranking method which is usually a 5 card high hand.
Sample 8 low hand.
The best possible 8 low hand is a wheel, an ace to five straight.