By the name I figured it to be something that makes sure that each team has an equal (relatively equal) number of living players on each team. However, I've been on numerous matches that have this supossed "Force Team Balance" where one team has 4-6 players (Resistance) while the other team has 2...

while the game is great, i find that some things are... not entirely implemented as well as they could have been. force team balance was likely one of those. hopefully the dlc and an update will fix that.

I've noticed that sometimes it won't let you switch to the team with more players... but that's sometimes...

I also noticed that when you join a friend it puts you on their team... possibly pub stompers?

It seems to be less of a "force" and more of a guideline

Don't forget also... if you join a game where half the team has quit out then you might just end up on the small team