Final answer:
In a powerlifting competition, all three judges, including the head judge and the two side judges, are responsible for determining if the bar stopped during a deadlift attempt. They use a system of lights or flags to signal their observation. The lift is unsuccessful if two or more judges indicate that the bar stopped.
Step-by-step explanation:
During a deadlift attempt in a powerlifting competition, determining if a bar stopped on the way up is a responsibility shared by all three judges: the head judge and the two side judges. Their collective role is to ensure that the lift is performed according to the competition rules, which typically state that the bar must be lifted in one smooth motion without stopping or hitching.
If any of the judges observe that the bar stopped during the lift, they can signal this by showing a red light once the lift is completed. This is often done using a system of lights or flags. If two or more judges show a red light, the lift is deemed unsuccessful due to the bar's stopping midway.