In a basketball game, defense is more stable and invariable than offense. The basic principles of man-to-man defense that defending offensive with ball are defender move on the straight line between offender and basket ring. The defender should move close enough to prevent offender's shooting, passing and penetration with ball (triple-threat). Oppositely, other four defenders guarding offenders without ball in the field have to change their defensive positions and stance as the ball moves. That is more important for the team defense than defending with ball. This study introduces defense without ball and important principles about it.