The kendo referee’s rulebook describes zanshin as one of the necessary elements of a successful yuko datotsu. In simple terms zanshin is the mental state and physical posture that allows you to respond to a counterattack after you make a strike. If zanshin is not present after an attack in shiai, the point is either ignored by the referees or results in tori keshi, where ippon is awarded and then taken away.
Typically zanshin is the process of going past your opponent after an attack and once you are in safe distance, turning to face him or her in chudan. If you are unable to go through then you need to have the tip of your shinai pointed firmly at their throat or centre.
Most kendoka are aware of the need for zanshin, but many of us do not incorporate correct zanshin into their basic kihon training or in some cases jigeiko. To work it has to be practiced an essential part of each technique and not occasionally switched on when required. I often see examples where after a good men strike, the attacker will relax as he or she moves through after striking. You can almost sense a feeling of relief as chudan is dropped as they move past their opponent. I have even seen players release one hand from the shinai after striking.
More often this lack of zanshin is manifested by a slowing of pace and loss of posture after the attack. Another clear indication that zanshin is not present is where a player takes a number of steps forward past their opponent, turns and takes chudan kamae whilst stepping backwards. This is obviously a weak position and he could be easily overwhelmed if his opponent made a strong forward attack at this time.
To ensure that zanshin is there when you need it, you should practice it as an integral part of each technique, even in the most basic of drills. So for example in men uchikomi geiko you should step forward into your opponents distance, strike men, take 3 or 4 steps past your partner, keeping the tip of your shinai forward, then turn, stepping forward in chudan into correct distance. This forward movement should be assertive to the point of becoming your next seme.
Correct kakarigeiko is a great way to develop zanshin as you work on a pattern of seme, strike, go through with correct zanshin, turn, move forward into seme and strike again. If practiced this way zanshin becomes an integral part of each technique, not an additional element for use in shiai or grading examinations.