Definition: A block bet or blocking bet in poker is a bet made that is very small in relation to the pot. Its usually a term used to talk about making a small bet on the river to get to a cheap showdown out of position, instead of checking to your opponent and potentially calling a large bet.
Your hand is JQs, your opponent raises from the button preflop, you call from the big blind. The flop comes down J – K – 2. You check, your opponent makes a continuation bet, you call, turn comes a 5, you check, your opponent checks. Now the river comes a 6, your not sure if you have the best hand, but if you do, your opponent wont call a massive bet, so you decide to make a small blocking bet to try and get some thin value and get to showdown cheaply.
The biggest problem with the blocking bet is it makes your hand look transparent to being a weak made hand (Which it almost always is) and can induce bluff raises. Also, if your playing against someone smart you will have to make block bets with stronger hands to avoid getting exploited by your opponents, when you would frequently want to value bet your strong hands larger.
However, the counter argument to this is as follows: your opponent rarely has anything better than Jx. So whenever you can beat Jx, you can make a block bet as a value bet because your opponent will not frequently have a strong hand. Also, you can make it with your weaker Jx range/missed draws that you played slowly. This will in effect balance your whole range so you will have a slew of hands from missed draws, to Kx, to Jx, all played in the same way and your opponent will not be able to peg you on a certain hand when you reach the river and make a small bet.
I could also argue that, in this spot your opponent will not frequently bluff you, especially if there are not many missed draws, if there are lots of missed draws I would argue for a check call on the river and hopefully your opponent will put you on either a weak jack or a missed draw and try to take you off it. If there are no draws I would recommend that you just check fold because your opponent will not frequently bluff you. This is something a lot of new players find hard doing because they think there hand is too strong to check fold on the river, but in reality, you beat no bluffs and it looks like you have a made hand (So your opponent wont bluff too frequently).
Again, everything is situational, you can check call against some players if you think there bluff frequency is huge. I wouldn’t worry about getting exploited by check folding too frequently, id be more worried about getting exploited by donk betting and getting bluff raised and not knowing what to do.
Whatever you decide, block betting in poker is something you should add to your arsenal. Against different opponents with the same hand and same situation you could argue for a check call, a check fold or a block bet. Figuring out exactly what you should do against each opponent is your challenge!