Defense Against the Semi-Bluff - The Power of the Semi-Bluff

Let's say you're playing seven-card stud. You have a pair of jacks, and on fifth street your opponent bets. You know he has a big hand. So your response is easy: You fold. Suppose you know your opponent is bluffing with nothing. Again your response is easy: You raise. Suppose you think he has you beat with two small pair, but you're getting sufficient pot odds for a call. So you call. Straightforward bets, straightforward responses.
But what if your opponent is not so straightforward? What if he's the kind of player who might be betting with a legitimate hand but might also be semi-bluffing? He's not always semi-bluffing, of course. That would also make it too easy to respond, because if you know an opponent is semi-bluffing when he bets, you can simply raise with anything, and he will probably fold. The problem arises when you think an opponent may be semi-bluffing but can't be sure he does not have a legitimate hand. What's more, if he doesn't have a legitimate hand now, he may get it later - or he may look like he's gotten it later.
It turns out there aren't many defenses against the semi-bluff, which is why it is such a powerful play. Frequently the best play against a possible semi-bluff is to fold, especially when the pot is small. All right, your opponent has beaten you. He may even have made you throw away the best hand. But if you call his bet, he has three other ways of beating you. He may in fact have had the best hand when he bet. He may have been semi-bluffing, but he now outdraws you. Or he may have been semi-bluffing, but he proceeds to catch scare cards that force you to fold. Therefore, though you may have thrown away what was the best hand at the moment, still your opponent had too many ways of beating you to justify your calling his bet.
Even when you think you are favored to have the best hand, it may be correct to fold. Let's say you think it's a little better than even money that your opponent is semi-bluffing. For convenience, we'll say you think there's a 52 percent chance he's semi-bluffing and a 48 percent chance he has a good hand. If he is semi-bluffing, you figure you're a 6-to-5 favorite to beat him. However, if he isn't semi-bluffing and has the hand he's representing, you're virtually locked out. Thus, 52 percent of the time you're a favorite to win. Should you call his bet? Many professionals as well as amateurs make the mistake of calling in such situations, but unless the pot is large, the correct play is to fold.
Let's work it out mathematically. You lose almost automatically 48 percent of the time. Of the remaining 52 percent, you'll win an average of six out of 11 hands (since you estimate yourself to be a 6-to-5 favorite). In other words, you'll lose almost half the time when you're a slight favorite and virtually all of the time when you're a big underdog. You stand to win the hand only 29 percent of the time in all. To call the bet then, you would need to be getting at least 7-to-3 effective odds from the pot, which is not very likely in an early betting round. Hence, the correct play would normally be to fold.