I didn't mean to full on grapple a bear with one hand, generally meant to use an open hand to vault over terrain or use items or something. It's kinda hard to explain I guess.
I assumed at first you were thinking sth like using the offhand to break/open/dismantle someone's guard/stance? While that's a thing in HEMA, generally youd be better off doing so with a tool since that provides more reach.
As for vaulting over terrain, unless the terrain is very steep youre unlikely to need more than your legs (and good ankle protection ig). You'd be amazed how well your torso can balance in fucky terrain.
Using items like throwables/explosives with your off hand makes sense, and it's quite common in various mangas already.