Answered April 17th, 2019

Roger Clemens pitches in Fenway Park for the first time as an opponent, striking out 16 in a 3-1 Blue Jays victory. The 16 Ks tied Jack Harshman's 1954 record for most by an opposing pitcher at Boston.

Which pitcher has the most Ks in a game at Boston?
Interpreted as:
Which pitcher has the most Ks in a regular season game at Boston?