This article looks at the middle stages of a Sit & Go tournament - from around the fourth blind level to the point when only four players remain. If play gets down to only four runners in the first three levels, there is no middle phase, but this rarely happens.
When the blinds are big and your stack drops under 10BB for example, you can't wait around for the next category 1-2 hand. Instead you should be willing to raise or push with a wide range of hands, in order to stay in contention and make it to the bubble.
You can avoid losing chips by folding trash hands, expecially when in the blinds. Don't play passively at this stage. Instead raise with any two cards when in a good spot if you have 5BB or less. It's better to go out fighting with a fair chance of doubling, as opposed to being tight and getting eaten by the blinds.
When you raise for a third of your stack or more, you have committed so many chips that you have to be willing to get the rest in. Therefore its perhaps better to push all-in pre-flop, instead of making a big raise. This will not only put pressure on your opponent but also increase your chances of a double up (providing you have a strong hand). If you are raising post-flop for a third of your stack, you should do so with the idea of getting the rest in on later streets, even if there are scare cards on the board.
This is based on the power of aggression - one of the core concepts in No Limit Hold'em. By pushing all in you have two ways to win the hand. Your opponent can either fold, or they can call, which means you still have a chance to win at showdown. This is the reason why you can push with more hands than you can call with. If your opponent pushes all-in you may have a difficult decision to face and can make mistakes, either by folding the winning hand or calling while way behind.
The size of your opponents stacks is one of the most important factors in playing your way through a Sit & Go. You should be willing to get involved with smaller stacks but avoid the bigger ones. The reason for this is that a big stack can bust you and is more likely to give you action. They will also put pressure on you with raises or reraises that put your tourney life at risk. A short stack will be more likely to fold however, unless they have a good hand that they think they can double through with.