I have always found that the easiest time to hit someone is when they step back. This is normally because in the act of doing so, they break concentration and lose their kamae. Theoretically, if your chudan is correct it is impossible for an opponent to strike you. However when you step backwards, particularly when you do so to avoid your opponent’s pressure, you risk moving the point of your shinai from the centre. This is a perfect opportunity for your opponent to attack men. It is surprising that even strong players make this mistake. In most cases they do so to give them sufficient distance to make their own attack, but once they are on the back foot, it is relatively simple for the other party to take an extra step forward and strike.
It is not difficult to avoid this problem, simply do not step back. If you think about keeping the point of the shinai forward at all times it is easier to apply counter techniques and the worst that can happen is that you both move forward into tsubazeriai. Now you can move back safely into fighting distance, but do so watching your opponent and covering his shinai. Most importantly ensure that you keep your left heel off the ground, as once your heel is planted you are unable to move in any direction and again become an easy target.
I realise that this advice is taking a somewhat negative tone in being a list of things not to do. Looking at it in a more positive light, your objective is to keep moving forward. Constantly take the fight to your opponents half of the court or practice area and break his or her posture and kamae by strongly stepping into their distance. When we talk about this, the question most often asked is “what happens if your opponent also comes forward”. This does and will happen, but your mind set should be that you will dominate and if you really believe that, the chances are that the other player will crumble under the pressure.