Complex sentence: Fisk was reportedly among a group of several Red Sox players who lobbied Boston management for players to be paid what they deserved, which made him none too popular with Haywood Sullivan, the Boston general manager.
Split into simpler sentences: Fisk was reportedly among a group of several Red Sox players who lobbied Boston management for players to be paid what they deserved. This made him none too popular with Haywood Sullivan, the Boston general manager.