Blockers For Beginners: Part II

This column will continue the discussion of blockers and unblockers, from my previous column in issue no. 14.

This time, let’s look at a river situation in which you have a bluff catcher and are thinking of calling your opponent’s pot-sized river bet.

Before we can enter into a detailed discussion of how blockers effect your decision, it is important to review another concept, which is MDF.

MDF is an abbreviation for Minimum Defensive Frequency, which is a fancy term for the fact that a successful player must not overfold. If you fold too often, your opponent can show a profit by betting any two cards.

To prevent this, you must call or raise a certain percentage of the time, and that percentage is your MDF. Life would be simple if there was one MDF that applied to all situations, but like almost all poker concepts, MDF can be complicated. An MDF is extremely difficult to calculate when there are more cards (and potential bets) to come. Also, it is further complicated when there is more than one defender in a multiway pot.

Another major complication is that the value of the bettor’s range is never absolutely clear. Does his betting range include only hands that beat all of my range or lose to all of it? In reality, his worst value bets may be weaker than my best bluff catchers. MDF also depends on their bet size. If all their value bets beat us and all their bluffs lose, it is easy to calculate the MDF for any bet size.

Here is an example: Your opponent raises in middle position and you call from the big blind. The flop is K Q 8. You check, he bets, and you call. The turn is 2, and again it goes, check, bet call. The river is 7. Again, you check, and he now makes a pot-sized bet.

When he makes a pot-sized bet on the river, GTO states that he should have two-thrids value bets and one-thirds bluffs. Your MDF is 50%. You must call at least half the time to prevent your opponent from being able to profitably bet any two cards.

Let’s say your bluff catcher includes a queen. You can’t beat any value bet from a hand that is at worst a pair of kings, but you beat all bluffs with hands that can’t beat your pair of queens. (Feel free to skip all the math and jump to the conclusions at the end.)

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This may seem confusing and artificial, but at least the numbers are in the zone – 76 value bets and 38 bluffs.

Now let’s look at two hands you might have as bluff catchers and see what they block. First is the A Q and second is Q 9.

A Q blocks about 12 of his value bets, but also 16 of his bluffs. Now his ratio of value bets to bluffs, 64 to 22, has increased from 67% to 75%. He is more likely than usual to be value betting, and you should fold your hand.

But Q 9 blocks about seven of his value bets and none of his bluffs. Now he is bluffing 36% of the time, instead of 33%. He is over-bluffing and you should call, even though Q 9 is a weaker hand.

In summary, fold more when your hand blocks his bluffs more than his value bets. Call more when your hand blocks his value bets more than his bluffs.

I want to add my own caveats: This applies to someone who is attempting to play GTO. If they bluff too much, you should generally call. If they don’t bluff enough, you should usually fold. If your hand is under-represented, they might think your hand is weaker than it is, tend to call. If your hand is over-represented because you’ve played as if you have a stronger hand than you have, you should tend to fold. ♠

Steve ‘Zee’ Zolotow aka The Bald Eagle or Zebra is a very successful gamesplayer. He has been a full-time gambler for over 40 years. With two WSOP bracelets, over 60 cashes, and a few million in tournament cashes, he is easing into retirement. He currently devotes most of his Vegas gaming time to poker, and can be found in cash games at Aria and Bellagio and at tournaments during the WSOP. When escaping from poker, he spends the spring and the fall in New York City where he hangs out at his bars: Doc Holliday’s, The Library, and DBA.