Complex sentence: In 1891, his father moved his family from their Ohio farm to Los Angeles, California where the powerfully built and athletic teenager boxed as an amateur until age 20, when he started fighting professionally.
Split into simpler sentences: In 1891, his father moved his family from their Ohio farm to Los Angeles, California. As a powerfully built and athletic teenager, Jeffries boxed as an amateur until age 20, when he started fighting professionally.