Complex sentence: With Bill Scott injured, Frank Butler took the ride, and Cotherstone started the 4/6 favourite against eight opponents, having drifted out from 1/2 just before the race as a great number of bets were placed on his stable companion Prizefighter.
Split into simpler sentences: With Bill Scott injured, Frank Butler took the ride, and Cotherstone started the 4/6 favourite against eight opponents. His odds had drifted out from 1/2 just before the race as a great number of bets were placed on his stable companion Prizefighter.