The first name can be any one of the seven. Then for each one . . .
The second name can be any one of the other six.
Total number of ways to pick 2 names = (7 x 6) = 42 .
BUT ...
If you pick Tom and then Jim, you have the same team as when
you pick Jim and then Tom.
Out of the 42 different ways to pick 2 names, each different team
can be picked in two ways.
So there are really only ( 42 / 2) = 21 different teams possible.