Complex sentence: While talking to Sandy, he is approached by Trenton's Pride and Ruffshodd, now fully-grown and Stripes' tormentors; the former challenges Stripes to a racing match at the Blue Moon Races, a Thoroughbred gathering.
Split into simpler sentences: While talking to Sandy, he is approached by Pride and Ruffshodd, now fully-grown and Stripes' tormentors. Pride challenges Stripes to a racing match at the Blue Moon Races, a Thoroughbred gathering.