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There is no defense that can be used against a good aggressive no limit player in position who is careful to adjust his frequencies. However very few players know just how much aggression is required in given situations. Many players often take it far too far and are not selective enough, or are aggressive in situations where are more passive approach will do better. The key to defeating aggressive opponents is to discover the weakness in their game and ruthlessly exploit it.
Play the percentages
Quite often they will either have no grasp of the basics, (or ignore them) and frequently put far too large amounts of their stack in preflop with bad hands. The way to beat players like this is not to try and ‘outlag' them, but to play the numbers game and make sure that on average your hand is a lot better than theirs is when you clash. Try and get as much money in preflop as you can, to maximize the mistakes they are making.
Don't raise yourself into a tricky position
Be careful not to commit an awkward amount preflop with hands like AK or 88. With these you either want to commit yourself preflop, or leave the pot relatively small so that you can get away from the hand if you need to.
Against players who are very aggressive after the flop, you need to develop a strategy that plays very big pots when you have great hand, and maximizes the chances of them bluffing you when you have an ok hand. Don't turn your great hands into bluff catchers, you should bet these and hope you get raised. It's much easier to do this in position than out of position, so try and always get position on a LAG. Sometimes even a mediocre player playing very aggressively can totally disrupt a TAGS game if he has position on him.
