Frying pans get a lot of use as improvised weapons in fiction, but how effective would they actually be?
The major thing to remember is: It’s not a weapon. They’re designed for cooking food, not bludgeoning people. Now, if you have a single piece of cast iron, that’s going, probably, hold up pretty well from clocking someone, but it will fare poorly against an aware opponent.
The major things the frying pan has working for it are the weight and that it’ll probably survive a hit. The downside is, it’s remarkably easy to defend against, if the victim sees it coming. It doesn’t have much reach, and the weight isn’t conducive to actual combat. Again, this isn’t a problem as a frying pan, because you’re not supposed to be hitting people with it.
So, how effective would it be? Not fantastic. It is an improvised weapon, meaning you wouldn’t use it if you had access to anything better, but if there really is no other option, it’s a solid chunk of iron that could be used to clock someone (depending on the design), but it’s a first step towards getting a real weapon, not something you’d want to use more than once.