How should I spot someone for a power clean?

Physical spotting is not recommended for the Olympic lifts. Due to the explosive and dynamic nature of the lifts, it is generally advised that only one person be on the platform at any one time. Instead of spotting, new lifters are taught how to dump the bar in case of a bad or missed lift. For a bar that is in front of an athlete, it is advised to push against the bar and step back to avoid it. For a bar who's path is traveling behind the lifter, it is advised to push against the bar and move forward to avoid it.