edit my last post: *and NOT about experiencing the game*
(something i, and others with me, consider a bad game design)
So, in your (example-?)game players would choose red or blue sometime while signing up, and then from that point on, they would play for that side whenever battling ?
Important question: are both sides different ?
if the answer is no, then i see no reason why not let them make their own teams and have teams play each other.
(this can be done through teams-for-this-one-game or a longer existing team that play many many games, or both)
If both sides are different, then players will naturally want to enjoy the other side as well,
i suggest giving them a character for both sides at the beginning(one account, two characters, easy to monitor, obviously only one character may be active at a time)
having a certain level-up/unlock system that will take a lot of time(making it hard to level-up a character on a second account, make sure this does not interfere with gameplay for newer players, make it some kind of newbie-protection)
One game i played, (it did not have two big teams) people could farm wins as much they wanted.
Ranked games showed their winrate, and some people had a 80-90% winrate, yet, most players in the community would recognize the "good" players by their winrate,
which was usually around 70%.
Now, i think most players with a 90% winratio didn't use multiaccounts, since there were plenty of other ways of screwing around
(make game, only allow people with less then 100 games finished join) but that's not the point.
Those farmers were looked down upon, which meant that they did their things to get their winrate up, and instead of fame they got shame