Answered May 3rd, 2019

George Hill posted 21 points off the bench in Game 3 of the 2019 Eastern Conference Semifinals against the Celtics - the most by a Bucks reserve in a postseason game since 2003.

Who was the last Bucks player with 21 points in a playoff game off the bench?
Interpreted as:
Who was the last Bucks player with 21 or more points in a playoff game off the bench?