Udat, I mean
Bev strikes me as a woman who practices some sort of self-defense hand-to-hand combat on her off time, and we know Janeway does.
Short of "just because", they really have no reason to fight. However, they're physically well matched, and I think it would be a good fight.
I'd also like to see Worf and B'Elanna pair off for a fight. I have no idea who would win, though.
Janeway would mop the floor with Beverly.
Janeway has most likely had more physical combat training than Bev., plus Janeway has a take no prisoners attitude.
Be'Lanna beats Worf because she's got guerilla warfare tactics. She's allot more clever than Worf.