Blocker

1. In community card poker games, such as Hold'em and Omaha, cards you hold that would be outs for your opponents.

Example

Let's say you hold 789T, all hearts, in a game of Omaha. If the flop comes 4h-5s-6h, and you get all-in against an opponent with the nut flush draw, you hold four blockers. In actuality, your hand gives you five blockers, because the 5h would make you a straight flush. So in this case, with two cards left to come, your opponent's chance of hitting a flush goes from roughly 35% (9 outs) to 16% (4 outs).

The Concept Explained

The main point about blockers is that you should be aware of them at all times, and also try to play hands that are likely to have blockers. It might go without saying that 88TT is a more valuable hand than 8822, but on a 783 flop, it becomes more obvious. Top set is still top set, but when you hold 88TT, you have blockers to an opponent's wrap draw (a hand like 6TJ or 569). In this case 569 is more likely because you hold two tens. Take a look at the numbers vs. a wrap draw with 88TT and 8822:

Board: 7h-8c-3s - {8h8dTsTh} = 58%, {5s6d9s2h} = 42%

Board: 7h-8c-3s - {8h8d2h2d} = 53%, {5s6d9s2c} = 47%

As you can see, when your hand has blockers it's 5% more valuable, which in the long run is a fair amount.

Blockers often influence Omaha hands, because the money usually goes in with the outcome very much in doubt. For example, when you flop a straight, you're probably only going to get action from two pair or better. So let's say you flop a straight with 9T on a 8JQ board and get it in with QQ. There is a big difference between holding 9T34 and 9TJ8:

Board: 8h-Qc-Jd - {9sTh3c4d} = 63%, {QdQs3s4h} = 37%

Board: 8h-Qc-Jd - {9sTh8cJs} = 71%, {QdQs3s4h} = 29%

In this instance, having blockers makes an 8% difference. So overall, it's extremely important to be aware of blockers and how they can help your game.