After seeing vids of Black Ops 2 and Playing a bit of BF3 made me realize how would I force teamwork in these games.
1. No regenrating health, One shot one kill and if you live through the first shot you are wounded and you will not be able to run.
2.You die you will not respawn and you have to wait until the round is over and play in round 2.
3. No Unlockables, it forces gamers to grind like Spaming grenade launchers a number of times to unlock something.
The first 2 would really work because they deemphasises running and gunning and promotes slower, strategic, cover and flank gameplay.
Actually, the results of the first two would probably result in nothing more than sniper spamming.
You can't force teamwork. You can encourage it by giving people an incentive to play different classes as they should...the best example of that is probably Team Fortress 2. People actually will play medics as healers, for example, because they're rewarded for doing so.
Rewards go a Hell of a lot further than restrictions and penalties.
It didn't used to be that way though. There was a time when people either played or did not play a game based on whether or not it was simply fun. Now a lot of games have these reward structures involved. When did it become necessary for that? Why do people have to 'earn' things in a video game? Nothing is really ever earned by playing video games anyways, unless you think obesity and lack of a social life is a reward, since most of the reward structures (especially those in MMOs) are massive time sinks to keep you paying and playing.
As far as the original topic goes though, I think objective based gameplay is the best way to encourage teamwork, but even that isn't a perfect solution. But at least, if you're playing a mod of a game where gaining objectives (like taking over nodes ala Onslaught mode in UT2k4), most players will have to participate in the team effort in order for your team to win. Also, keeping the game focus away from your own personal contribution (such as not focusing so much on individual damage or total individual kills) and placing more on the overall team contribution, would probably help.
Games like Tribes: Ascend do that to an extent. That game is a reward focused game, but you get more experience (used to buy rewards) if your team actually wins, so it's beneficial for each person to help the team as much as possible so that more points are earned and thus more individual rewards can be purchased. It also helps that in the case of Tribes, it's a team game by nature since it's primary focus is capture the flag, which falls back on my original point, that the type of mod played will have the greatest impact on teamwork most likely. It's going to be hard to get a bunch of people to care about teamwork in team deathmatch, or something similar, where all you really do is run around and focus on shooting other players.
Dae6 posted his while I was typing mine up, but what he's saying is along the same lines of what I was getting at by having less of the focus on the individual contribution. So, I agree with what he's saying, though it probably wouldn't be very popular. The namesless thing isn't quite as critical as simply not keeping track of statistics, because if you're completely nameless, than you wouldn't be able to make friends in the game and possibly form a group of 'regulars', which often happens in the online FPS's.