I recently watched an anime called Drifters, and a scene in E3 interested me. The protagonist pinned an enemy captain down and continuously rammed the tip of his nodachi scabbard into the captain's face; ignoring all the other unrealistic fight scenes for that show, is this type of tactic plausible? The protag did it to simply hurt the captain and keep him stationary for a few minutes for something else, but if your scabbard was solid enough, could you use it as a last resort weapon?
Not really, “as a weapon,” but it is possible to use a ridged scabbard somewhat creatively in combat. Mostly I’m thinking of using one as an improvised parrying tool. Though there are some other potential applications. For example: Blocking an incoming strike with the scabbard and then striking their swordarm with the blade.
Poking someone with the scabbard is technically possible, but there isn’t much point. Nothing prevents them from grabbing the scabbard in retaliation, and it’s not going to be doing any appreciable damage. But, if you really want your character to aggressively annoy someone, then it is one of many options.