Complex sentence: Benko was not a full-time professional chess player (he worked as an investment broker in New York), and his lack of practice against grandmaster-strength opposition and his tendency to get into time trouble weighed against his chances.
Split into simpler sentences: Benko was not a full-time professional chess player (he worked as an investment broker in New York) which limited his opportunities to play against grandmaster-strength opposition. In addition, his tendency to get into time trouble also weighed against his chances.