A blocking bet is made to block your opponents from raising you. This could mean that you would prefer your opponents either call or fold, but absolutely do not want them to raise you. It is the equivalent of boxing a player out in basketball, you can let them be a part of the action, but you want to remain in control and have the upper hand. If you are making a blocking bet it is assumed that you are first to act. You can’t make a blocking bet in position as it defeats the entire purpose. Blocking bets are crucial when playing pots out of position because when you are out of position you are almost always at a disadvantage. These bets are generally made on the flop, turn, or river and are not really applicable to pre-flop play.
Blocking bets should be made when you are unsure of your hand’s strength relative to your opponent. If you have the nuts making a blocking bet would be idiotic. A strong hand should be bet for value, where a weaker hand would implement a blocking bet. The times where you put out a blocking bet on the river are usually comprised of moderate made hands, where flop and turn blocking bets are often made to see a cheap turn or river. These flop and turn blocking bets that want to see a cheap turn or river are usually drawing hands. It is much more cost effective to make a small bet and get called than to check and be forced to call a much larger one. In addition to this is the fact that you taking the initiative in making a blocker bet allows you to have a bit of an edge when the next card is dealt. Check calling is often an indicator of a drawing hand whereas leading out can confuse your opponents and make it difficult for them to put you on a hand. Blocking bets should never be made as bluffs or for value, bluffs and value bets are two completely different concepts and should be played in an entirely different manner.
As mentioned previously, one of the biggest attributes of a blocking bet is its ability to make a hand more cost effective. There are a few reasons for this. If the blocking bet works to perfection on the river and you simply get called you may very well win the hand. If you had checked you might have been put to a tough decision as to whether or not to fold to their river bet. If the blocking bet is raised you will lose the least amount of money possible. Another bonus of a blocking bet is its ability to push people who have floated you out of the hand, the blocking bet will significantly reduce the odds of them bluffing at the pot.
When making a blocking bet you should always err on the side of caution. Make it on the smaller side no matter the scenario. If the pot on the river at .50/1 is $26, make a $9 blocking bet. Enough to get calls from hands inferior to your moderate made hands, but not so big that you will push them out. The same general bet sizing can be applied to flop and turn blocking bets made to protect your draw. If the pot on the flop is $12 and you have a strong draw at .50/1, an effective blocking bet would be $7. If you push the other player out, great, if not you will still have a chance to make your hand at a low cost.