Teamwork: Giving support to your team mates. This can be through healing, marking, reviving, cover fire, flanking, etc.
Good teamwork is having everyone on the team doing as many of these things as they can through out the match.
Yeah, teamwork is rare in games with randoms. You need to get a team of friends together, and ideally have a headset to form a strategy and co-ordinate efficiently. Move together (but not right next to each other), and have each other's backs. It's really just common sense, mostly.
I use the common sense thing. Talking and playing actually makes me a very sloppy player at any game.
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