Darcy elbowed Vlastuin in the face after he handballed the ball.
He was placed on report by the officiating umpire and the Tigers received a free kick down field.
The Tigers lead the Dockers at half-time 11.2 (68) to 3.5 (23).
Meanwhile, Harley Bennell has four disposals and has kicked two goals so far in his first game for the Dockers following the best part of two seasons on the sidelines due to ongoing calf issues.
Watch Darcy’s hit on Vlastuin in the video above.