Any cast executed properly will never do any damage to the rod. An overhead cast, done properly with the rod held at 90* will not be the cause of any problems. It is the mistake that is made when using this type of cast that leads to things on the line, beads, split shot etc. hitting the rod. The line will not intersect (tailing loop) itself either on the front or backcast 'if done properly". Having said that I would never teach anyone to do an overhead cast holding the rod straight up. I would have them hold it on a slight angle away from themselves for their safety and the rods safety, because everyone...did I mention everyone, makes a mistake sooner or later.