No idea. Banner/clan balance takes precedence. If a clan has 80% of the cavalry in game, they will be on the same team.
Happened the other day while I was on my 2 hander alt. Instead of despairing and losing though, we rallied around the 2 or 3 archers we had, protecting them from cavalry buttshanking and preventing the HX on the other team from bump shooting them.
We didn't wipe them out, but we got the MOTD to spawn everytime, took it over and won every round after losing the 2 rounds and being forced to get our shit together.
It just took about 3-4 vocal players on the same page giving out the same game plan and mocking the dumb ones who ran out to die.