Teaming is a verb, and is the act of working together as a team. It is a group of people forming a team in order to work together to accomplish a specific purpose, such as winning a game, unloading a boat, or pummeling a common opponent with snowballs. It’s almost always followed by the word “up”.
Teeming is an adjective, and is used to indicate that there is a crowd present, as in the teeming crowd, or the teeming station.
Remember which is which by knowing that it takes all the people to make a team. “All” and “Teaming” both have an “a” in them. On the other hand, if the people are just crowded together, use teeming, which crowds together two of the letter “e”.