Teaming in FFA occasionally gets out of hand (mostly OP 1.9). While many people assume FFA is a solo game mode, it's not necessarily so. FFA is literally just a game mode where you PvP to your hearts content. So this means you can kill whoever you want, whenever you want, and how you want. The only problem is if you are capable of doing so.
Teaming can get in the way, but that's only really an issue in the 1.8 FFA community. In Soup FFA, you can always get a good 1v1. I have no idea about normal 1.9. In OP, you can generally avoid getting into a massive fight with a team of 20 if you stay away from them/ not provoke them. In 1.8 FFA, there will be the regulars and randomly formed teams. Although majority of the regulars have left or focus on 1v1 these days, you will find them occasionally fighting together (which is kind of a problem, since most are decent at pvp). Then the random teams are the worst. I've seen a team of 15-20 that would not fight without one another.
To get this straight, I have nothing against teaming in FFA. I mean it's a never ending game mode, where you just mess around. If you enjoy playing FFA and want to continue it, then you might wanna consider having one team mate somewhere. Having a team version of FFA makes 2v2 duels (etc) pretty pointless. Not to mention, how would you sort the teams? Would one team always be imbalanced if there isn't enough players?