Complex sentence: His racing career began in 1949 at Riverside Park Speedway in Massachusetts; by the 1960s he was part of a group of Northeastern racers called "The Eastern Bandits" who moved to the Mid-Atlantic and South to compete in NASCAR competition.
Split into simpler sentences: His racing career began in 1949 at Riverside Park Speedway in Massachusetts. By the 1960s he was part of a group of Northeastern racers called "The Eastern Bandits" who moved to the Mid-Atlantic and South to compete in NASCAR competition.