Complex sentence: He then hit another grand slam on September 6 at Fenway Park against the Tampa Bay Rays, which tied a Red Sox rookie record, previously accomplished by Bob Zupcic in 1992.
Split into simpler sentences: He then hit another grand slam on September 6 at Fenway Park against the Tampa Bay Rays. That tied a Red Sox rookie record, shared by Bob Zupcic, who accomplished it in 1992.