Push or fold, a first approach

Sooner or later the blinds get to a point where your stack is 10 BB or less. From there, a raise commits too much of your stack to fold afterwards, and the only sensible moves left are all-in or fold.

This is the most studied spot in poker. The reference ranges are solved, and the exercises below will make them automatic.

Fold equity

A shove wins in two ways: when everyone folds, and when someone calls and you win the showdown. The first way is called fold equity, and it is what makes shoving weak hands profitable.

From the button with 9 BB, you shove close to a third of your hands, and more than half from the small blind once the button has folded, because the players behind you fold most of the time and you collect 1.5 BB for free. A hand like K7s is a clear shove from the button there.

Why not a small raise

With 9 BB, a min-raise puts in 2 BB, more than a fifth of the stack. If a blind shoves, you are getting such a good price that you have to call with almost everything, so you might as well have shoved in the first place and taken the fold equity.

Under 10 BB, the min-raise only makes sense with a hand that wants to be called and against opponents who never shove over it. That is rare enough that shove or fold is the right default.