When walking we can press "C" to go into a tactical stance where we have our weapon drawn and we can shoot "from the hip".
We can also use the main stance button "X" for crouch/stand while using the tactical stance on the move. However i noticed that when in one of the three standing stances we can no longer use "X" to go to crouch and back to standing during tactical stance "C" is used and we are on the move.
To give you an idea look at "Steps To Reproduce".