Historically, wooden shields seldom had a metal outer binding as the vanilla minecraft shield does, because a sword hitting a metal rim would just bounce off, whereas a shield with no rim or a leather-bound rim (which is what this one has) would allow a sword to cut into it, possibly getting stuck, allowing the shield bearer to either disarm the opponent or create an opening for attack. Obviously minecraft has no mechanics like this, but it's an excuse to make something that looks nice.