Complex sentence: He commenced a strong rail run going into the far turn but he had to be taken up and stedied by his jockey Jeremy Rose when a whole closed up on him and he lacked room to continue his run on the inside.
Split into simpler sentences: He commenced a strong rail run going into the far turn, but had to be taken up and steadied by his jockey Jeremy Rose when a hole closed up on him. At that point, he lacked room to continue his run on the inside.