Career
He played six seasons in Major League Baseball from 1871-1876 for the Chicago White Stockings, Troy Haymakers, Brooklyn Eckfords, Philadelphia White Stockings of the National Association (NA), and Athletic of Philadelphia in the National League. Zettlein began playing in 1865 for Eckford of Brooklyn in the National Association of Base Ball Players, the amateur-only predecessor to the NA. He joined the Brooklyn Atlantics in 1866, and remained with the team until 1870. In 1871, he joined the professional White Stockings of the NA, and in May 1871 he gave up the new league"s first home run.
He went on to give up the league"s first grand slam in September of the same year.
He had a record of 18-9 with a league-leading 2.73 European Research Area that year. The following season, Zettlein played for the Troy Haymakers and Brooklyn Eckfords, combining for 15 wins and 16 losses between the two teams.
Partway through the 1875 season, he rejoined the Philadelphia White Stockings, and ended his career in 1876 with the Philadelphia Athletics. He finished his career with 129 wins, 112 losses, and a 2.55 earned run average.