Complex sentence: Judges and timers are more commonly seen in local and non-professional events; the timer begins when horse and rider cross the start line, and ends when the barrel pattern has been successfully executed and horse and rider cross the finish line.
Split into simpler sentences: Judges and timers are more commonly seen in local and non-professional events. The timer begins when horse and rider cross the start line, and ends when the barrel pattern has been successfully executed and horse and rider cross the finish line.