Isolation bets are raises designed to thin out the field. You want to understand isolation strategies both to employ them in your own poker arsenal but also to recognize when someone else is employing isolation bets. So a standard isolation play might look something like, UTG limps and then there are two more limpers in middle position. Given the pot odds already, SB and BB are likely to limp to the flop regardless of their hole cards. So you’re on the button, look down on QQ, a pretty decent PP but not without a lot of risks. Against potentially 5 other players, you are likely to be holding the dog hand by the flop and you will be in a tricky situation. Therefore, button makes a big raise in the order of 5x BB to force people out of the hand and reduce the field to just 1 or 2 other players.
The aim of isolation bets is to reduce the number of players in the hand, typically the isolation play is pre-flop. The logic is that, certain hands fare better heads up or against fewer opponents. Usually you are talking hands like pairs, which are typically the mathematical favorite against non-pairs heads up. But pairs, especially medium and small pairs, become a big dog against 3 or more players. So it makes mathematical sense to always try to get into a heads up situation with pairs as it increases your EV.
Apart from improving your mathematical EV to the flop, isolation bets also give you information. Isolation bets are usually quite large and should be much higher than the standard 3x BB raise pre-flop. By just calling the isolation raise, it indicates the type of hands that the remaining players could be holding. Combine this with the player’s tendencies and the action on the flop, you should be able to put him on his cards by the turn.
The other strategic consideration for an isolation play is against an overly loose-aggressive player. These players tend to be raising pre-flop or at least getting involved in a lot of hands which necessarily reduces the quality of hands they are willing to play with. Therefore, when holding a quality hand there is again a mathematical advantage to getting HU against this kind of player. So beyond PP, AJ or AQ type hands are likely to dominate a player who raises pre-flop with ace-rag suited type hands. Getting heads up with him protects your advantage over him. So isolation plays can even be re-raises. In fact these make the best isolation plays because it is difficult for the remaining players to call when there have been two raises already.
Isolation bets also become common in poker tournaments, especially during the middle and late phases of the tournament. This happens because often short stacks will begin shoving all in on any pairs or marginal aces. If you are holding a big ace or big pair, there is a good chance you have the short stack dominated. If you do have him dominated, with a 3 to 1 advantage, you need to protect your edge. In this kind of scenario, instead of just calling and perhaps letting other players into the hand, it is better to raise again to shut everyone else out of the hand. This because even though you might be a 3 to 1 advantage against the short stack, letting other people into the pot -especially other people who might have position on you – reduces your odds of winning the hand.
Finally, the most important strategic use of isolation plays is to pick off the weak players. Once you have marked out the weak players on the table, you want to employ isolation bets to get into HU situations with them. Because you will be playing better cards and also be able to get him to fold a lot, it becomes a very profitable way to pick off his stack. You’ll see this kind of action on cash tables especially as the sharks tend to stay out of each others way and use isolation bets to signal to each other that they intend to claim this pot.