Answered January 12th, 2020

Since 1940, Mel Parnell has the lowest ERA by a Red Sox left-hander with 100.0+ innings pitched at home in a season, with an ERA of 2.29 in 1948.

lowest era in a season by a red sox lhp with 100 ip at home since 1940
Interpreted as:
lowest era in a season by a red sox lhp with 100 or more ip at home since 1940

See Trending MLB Searches