Complex sentence: But while American Pharoah fended off the challenge from Frosted, Keen Ice was coming up on the outside, also under a new jockey, Javier Castellano, and overtook American Pharoah at the sixteenth pole to defeat him by three-quarters of a length.
Split into simpler sentences: But while American Pharoah fended off the challenge from Frosted, Keen Ice was coming up on the outside, also under a new jockey, Javier Castellano. They overtook American Pharoah at the sixteenth pole, going on to defeat him by three-quarters of a length.