"Mazikin" means the actual damagers, and "Nizakin" are those who have been damaged. "Nezikin" means damages (types of damages), which is what the Mishnah is discussing.

(The Shitah Mekubetzes here points out that the Mishnayos in Bava Kama were written in the language of the Yerushalmi, as the Gemara says on 6b, and thus "Nezikin" is the appropriate term in Yerushalmi dialect; see there. Also, the Me'iri writes that the Tana chose to use the word "Nezikin" and not "Mazikin" because "Mazikin" denotes intention to damage, whereas the types of damagers mentioned in the mention include even unintential damage.)

B'Virchas Kol Tuv,

Eliezer Chrysler