I cannot understand the meaning of 手前 in the following sentence. As far as I know 手前 means "in front of my/your hands" or could be a pronoun. However I haven't seen before the usage like in the sentence below, so could you please explain the meaning.
"Because it is pretty rare to see a girl wearing kimono, my eyes unintentionally followed her. Our eyes met, she tighten one's jaw and right in front of me..."
~Edited: I think I'm more or less understand the meaning, thanks to Brandon. But I also can't figure out why it's used な here, as if 手前 is na-adjective?