In kendo, a valid strike must be made with full spirit and correct posture, with the striking part of the bamboo sword, and with zanshin, continued alertness after the strike. Article 12 of the rules for kendo matches and refereeing sets this out.
Under Article 27, the referees may consult and cancel a strike already declared valid if the competitor behaves improperly. The detailed rules name two cases. One is showing no readiness toward the opponent after the strike. The other is showing off the strike or its validity more than necessary.