The headword is in the genitive case, as it is in the phrase o)flhma a)naumaxi/ou ('fine for non-naval-fighting'). See also nu 64.
For the passage as a whole, cf. Lexica Segueriana 217.21 (which, however, reads "so also for *not* fighting at sea"). MacDowell (1962) p.111 and others have suggested that anaumachion describes the offense of a trierarch's withholding his ship from action. MacDowell further suggests that the offense may be the naval equivalent of astrateia, that is, that it may refer to a sailor's failure to join the navy when obliged. A further possibility (which I discuss in Hamel, 403-5) is that anaumachion is rather the naval analogue of lipotaxion, referring to a sailor's failure to board his ship prior to an engagement.
[1] The offense of astrateia.
[2] The offense of lipotaxion.
[3] The offense of rhipsaspia.
[4] Andocides (1.74 [Web address 1]) writes of those who are "found guilty of anaumachion": a)naumaxi/ou o)/floien. The appearance there of the verb o)/floien may explain the Suda's odd construction to\ o)/flhma a)naumaxi/ou. For the offense see also Pollux 8.40, 42-43.
[5] For a discussion of Andocides' treatment of atimia at 1.73-79 (Web address 1) see Hansen (1976) pp. 82-90.