He Had played for the New York Mets, Pittsburgh Pirates and Boston Red Sox organisations.

He was scouted by Australian national coach Tony Harris in 2005 and eventually signed with the New York Mets in 2005 at the age of 16.

In 2006, Welch made his Claxton Shield debut for the South Australia Bite where he went 0 for 1 with 3 walks.

Welch played for the Adelaide Bite of the Australian Baseball League (ABL) from 2010 to 2017.

After the conclusion of the season, Welch announced his retirement, leading the club in all time in games (284), hits (258), runs (160), home runs (35) and RBI (169) [9] Stefan attended Norwood Morialta High School and graduated in 2006[10] He also played cricket, football, and basketball for local Adelaide clubs and school teams.