Set up a team battle lobby (with any capacity or settings) and either:
A. Wait for anybody to join and launch it.
B. Invite a friend and launch it.
You don't need to finish the the match in order for it to count towards the achievement; every time you reach the character select screen for the first time you're making progress.
After the match ends (or any time after you've reached the character select screen) back out and create another team battle lobby, lather, rinse, repeat.
I recommend working on other achievements in the mean time (such as Superior Super or Ultra finishes/Perfect matches) or if you're like me and have all other easily obtainable achievements just stand still and let others get wins off of you so they can get some free wins to work towards "Teamworker."
* This works especially well if you and/or your friend need to get "teamworker." They can join in, get their 10 wins in 10 different lobbies and then you get your 10 wins in another 10 lobbies and you're already two thirds of the way to your achievement.