Complex sentence: While still in school Jansen started his baseball career playing semi-pro ball, but in 1940 was discovered by a scout and started playing for the Salt Lake City Bees, a Class C club at that time.
Split into simpler sentences: While still in school Jansen started his baseball career playing semi-pro ball. In 1940 Jansen was discovered by a scout and started playing for the Salt Lake City Bees, a Class C club at that time.