Fandom and the internet have their own set of rules, and in the case of Star Wars: The Force Awakens, we're seeing that in action every day. Aside from "'ships" talking about who they want to hook up in the series, the prevalent discussion has been around the stormtrooper wielding a Z6 Riot Control Baton (as identified in the Force Awakens Visual Dictionary) who fights Finn after uttering a single word: Traitor!
Fans have thus dubbed this character "TR-8R," a designation that when read aloud sounds like his lone line in the film. The character is an example of how the stormtroopers have evolved in the First Order since the days of the Empire. No longer can they be viewed as ineffectual canon fodder - there are some individuals in this army, and they, especially TR-8R are actually pretty badass.
As spotted by Slashfilm, the book "Before the Awakening," which includes prequel tales for Rey, Poe, and Finn, may offer us a clue as to TR-8R's real identity. In the story, we meet Finn's training squad, FN-2199 "Nines", FN-2000 "Zero", and FN-2003 "Slip." According to the Visual Dictionary, Slip happens to be the stormtrooper who dies at the beginning of the movie, painting a streak of his own blood down Finn's helmet and helping instigate Finn's journey and drastic changes.
The theory, then, while unconfirmed for now, is that TR-8R is in fact Nines of Zero. The deeply personal way the trooper shouts his signature line and the fact that he seems to know exactly how Finn fights does give some indication of that. Of course, it could just be that they're all trained that way, and this particular guy excels.
Regardless, it's a strong theory, and would certainly add a little more weight to the battle. It does beg the question why Finn wouldn't be a bit upset that his squadmate just got killed (while, granted, attempting to kill him), though.