The Hershey Chase experiment proved that DNA was the hereditary material rather than protein because they showed that when bacteriophages, which are composed of protein and DNA infect bacteria, their entire DNA enters the cell but most if not all of their protein doesn't, it is left outside the host cell.
Hershey and Chase subjected the phage attached to bacterium to violent agitation using a blender which removed the empty viral protein shells from the bacterial surface, thus proving viral infection was DNA related not (viral) protein related.