A fundamental mistake made by newer poker players is betting the river with a mediocre hand. Why is this such a costly mistake? Because when you bet a mediocre hand, you’re only likely to be called by a hand that has you beat.
Overall, betting a mediocre hand on the river, such as bottom or middle pair with a weak kicker, will lose you money. This play has what is commonly referred to as a negative expected value, or negative EV. When you bet the river with a mediocre hand, there are two likely outcomes:
Your opponent folds a worse hand, and you make nothing.
Your opponent calls with a better hand, and you lose money.
By checking down your mediocre hands, you will win the hands that are worse than yours (and not worth a call on the river), and save money on the hands he would have called your bet with.
So when should you bet the river?
1. You think your opponent has a worse hand than you do, and you’ll get a call.
If you suspect that your opponent has a pair worse than yours, or a weaker kicker, it’s a good reason to bet the river. For example, let’s say you decide to limp in early position with AJ. A couple of stragglers come in behind you. The flop is A84 rainbow. The blinds check and you bet out a ½ pot-sized bet. A late position player gives you a call, and everyone else folds. The turn is a 2. You bet out ½ the pot again, and he again flat calls. The river is another 4. Should you bet here? The answer to this question is yet another question: what do you think your opponent has?
In the absence of draws, if you have a read on your opponent’s play as being fairly passive, it’s probable that he’s in there with an Ace lower than yours. If he had A8, you’re fairly certain he’d have raised with it.
You decide through a read of your opponent, and his play up to this point that he is on AT. A bet here likely makes you a little bit more money. If you check, he will probably check behind you, so you have to lead out with a reasonable bet and hope he calls with his worse kicker.
2. You think your opponent has a better hand than you, but will fold to a reasonable bet.
Let’s say you’re on the button with 78 of hearts. A tight player in middle position limps in, and you follow along. The blinds flat call. The flop is A65 rainbow. The blinds check, and the limper bets 1/3 of the pot. Now, you’re getting 4:1 on your money to chase your well disguised straight draw so you elect to call. The blinds fold. The turn brings a Q, and the limper checks to you. You suspect he might have just been taking a stab at a bluff on the flop, or he might be weak here (small pocket pair, Ace with a bad kicker, etc), but you’re not quite sure just yet. You elect to take the free card off and make a decision on the river. The river brings a 2, and you’ve completely missed your draw.
Your tight opponent checks to you, again. What’s your move?
This is a perfect example of a time to bet with a nothing hand. Your opponent checked to you twice in a row, including the river (his last chance to make money off you). This almost always indicates weakness. If you check, you most certainly lose to his small pair, or higher kicker. Since he’s a fairly tight player, he’s not likely to call you down with a weak hand. Bet out something near the size of the pot (assuming it’s a moderate portion of his stack), and he’ll likely go away.
As you can see, making this simple adjustment to your game can make you a lot of money by ensuring that your good hands are paid off, your bad hands have a chance to win, and your mediocre hands don’t get you into trouble.