Whenever you hold a drawing hand in a community card game such as hold'em or Omaha, the process of calculating your outs gets complicated. Since the cards in the middle of the table are shared by everyone, a card that makes your hand could also make an even better hand for one of your opponents. These are commonly referred to as tainted, or contaminated, outs.
A prime example would be a straight draw on a board that contains two cards to a flush. Suppose you limp in from the button with J-10 off-suit. The flop is Q-9-3, with two spades. You've flopped an open-ended straight draw with eights outs to the nut straight. At first glance, it looks pretty sweet. But only six of those outs will actually give you the nuts, because the king and eight of spades are both tainted- they might give one of your opponents a spade flush. Naturally, the more opponents you have in the pot with you, the more likely it becomes that one of them will indeed make a flush when that third suited card hits. You can still draw, but you'll need better odds than you would if all your outs were clean.
And there are plenty of other ways that your draw can be tainted. Let's say you raise before the flop with A-K of hearts, get three callers, and the flop is J-Q-5 rainbow. You hold two giant overcards, but the only outs you have that are truly "clean" are the four remaining tens for a straight. An ace or a king will give you top pair with top kicker, but it could also give one of your opponents the Broadway straight. And since most hold'em players just love to play any two big cards, an ace or king on the board could potentially give one of your opponents two pair, which also beats you. Now you could make a bigger two pair by hitting your other hole card on the river, in which case the board would look something like this: J-Q-5-A-K. Of course now anybody holding a solitary ten would take the pot. If we put two diamonds on that J-Q-5 flop, it gets even worse because now the ten of diamonds has also become contaminated.
As much as tainted outs can be a problem for hold'em players, they can be downright treacherous in Omaha. Because in Omaha, with four starting cards to work with, players are much more likely to make the nuts for any given board, especially in a multi-way pot. Straight draws can easily be ruined by board that makes a three-flush, or worse, a board that pairs. Even drawing to a full house in Omaha can be problematic, unless you are certain that you are drawing to the nut full house. Consider that if you are drawing to a full house with bottom set, virtually every single one of your outs will be tainted-all except for that one card in the deck that could give you quads.
Drawing hands can be extremely seductive. It's always a great feeling when the dealer peels off one of the cards you were hoping to catch. But be wary of those tainted outs. The card that hits your hand could very well hit one of your opponents even harder. Keep that in mind whenever you're drawing, and always pay attention to see if any of your outs are contaminated. If so, don't count them as full outs, and look for better pot odds if you want to keep on playing.
