The Dwarves (The Hobbit) vs The Fellowship of the Ring (LOTR)
During their respective visits to Rivendal a time paradox happens that cause both groups to get magically transported to Goblintown. The town is completely devoid of life now. The characters have a spell that has been put on their eyes that make them see the other group as Goblins and Orcs and they can not understand each other.
Obviously they don't hesitate and begin to fight. Gandolf being magical himself was able to resist the effect and is not in the fight but he and everyone else is powerless to oppose the time paradox effect.
Team Dwarves:
Thorin
Bifur
Bombur
Gloin
Dori
Balin
Oin
Nori
Bofur
Dwalin
Fili
Kili
Ori
Bilbo Baggins
Team Fellowship:
Aragorn
Legolas
Gimli
Boromir
Frodo
Sam
Merry
Pippin
If this seems unfair we'll say Faramir was there and no one noticed and got sucked in to. If it's still not fair we shall add the fat elf that gets killed in the two towers(I can't remember his name), Theoden, Eowyn, Eomer, Arwen(Not allowed to use Magic).