A high speed (1000 frame/s) video segment, 0.367 seconds long, showing a territorial male Pachydiplax longipennis dragonfly responding in the field to a challenge from a conspecific male, reveals that the defender used a high rate yaw-turn to position itself to drive off the challenger. In-phase flapping of the fore and hind wings was used during the yaw turn and in the following pursuit of the challenger. During the right yawing turn, the dragonfly flapped its right wings to a more negative stroke amplitude than its left wings on the first two downstrokes (1^st downstroke: -65° right wing, -45° left wing; 2nd downstroke: -90°right wing, -50°left wing). Upstroke amplitudes were the same for both wings throughout the yaw turn. The 135° yaw turn was executed, in three wing beats (0.085 s) and in about 6/10ths of a body length of horizontal travel, at an average yaw rate of 1590%., and a peak turn rate of 3000%. This rapid yawing rotation was accompanied by a significant deceleration in flight path speed, which dropped from 30 to 7 body lengths per second (1.1 m/s to 0.3 m/s) as the dragonfly yawed through 90°in the first half of the yaw turn. The wingbeat frequency dropped from 41.7 Hz at the beginning of the yaw turn to 33.3 Hz at the end. The horizontal and vertical flight velocity components both reached zero near the completion of the yaw turn, during the upstroke portion of the third wing beat. Within 1/10th of a second after completing the yaw turn, the defender had reached speeds of 8 body lengths per second (0.3 m/s) upward and 14 body lengths per second (0.55 m/s) horizontally, and was accelerating along its flight path at approximately 150 body lengths per second² (5.5 m/s²) in its pursuit of the challenger.