So, I was looking up Fighter subclasses in D&D 5e, and I came across a website called Giger's 5e D&D. In it there is a subclass called Fencer, and I was wondering if it's Unearthed Arcana or pure Homebrew.
It is homebrew.
There is no official subclass (or any feature actually) called Fencer in any officially published book or UA. So this must be a homebrew created by someone outside of that.
As for citations, I did a deep search of all the UA material for the term "fencer" and it never comes up as a class option. A similar search on D&DBeyond also turns up nothing.
This subclass for the fighter is a homebrew. Someone talked about making a fencer homebrew subclass on reddit, however I do not know if they made this one. The subclass is not listed in any official D&D 5e books so it is a homebrew.