Nick Anderson had 50 points off the bench versus the New Jersey Nets on April 23, 1993.

who is the first player with 50 points in a game off the bench
Interpreted as:
Who is the first player with 50 or more points in a game off the bench?
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4/23/1993Anderson4/9/2019Crawford5051
NAMEDATETMOPPPTSMINREBASTSTLBLKTOVFGMFGAFG%3PM3PA3P%FTMFTAFT%PF+/-
Nick AndersonNick Anderson4/23/1993ORLORL@NJNNJN503332201172568.04757.11212100.01
Jamal CrawfordJamal Crawford4/9/2019PHXPHX@DALDAL513855114183060.071353.88988.94-5
Results may be incomplete. StatMuse has complete game-level data for games started going back to the 1981-82 season.