Weimer emerged as one of the Chicago Cubs' top starting pitchers in the first part of the 20th century. He went 21–9 with a 2.30 ERA in his 1903 rookie season and 20–14 with 1.91 in his sophomore year.
Weimer rose to become one of the Chicago Cubs' leading starting pitchers in the early 20th century. He achieved a notable rookie season in 1903, going 21–9 with a 2.30 ERA, and followed it up with a successful sophomore year in 1904, recording 20–14 with a 1.91 ERA.