official scorer (1872)

“If the official scorer would be a little more obliging to the reporters and remain long enough on the ground to allow them to obtain details from their books, it might make the latter feel happy and save them ‘a heap of trouble.'” “Base Ball: Second Championship Game Between the Baltimore and Cleveland Clubs,” Inter Ocean (Chicago), May 31, 1872, p2

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1877.  “The official scorer was appealed to, but he being a Cincinnati man, of course gave such information only as was favorable to the Reds.” (The Boston Globe, May 19; Peter Morris)