I am working on the option to register and run as teams in the Run4Fun application. Below you can see some work in progress. First I added a new segment on the event page:

The Register a team button will open a dialog:

The name field has a validator to prevent double entries. You can initially add team members to the team for convenience. As a result the team with its members is being displayed in the table:

This field contains runners that signed up for the event and are not member of a team for this event. (so you can sign up for multiple teams but only 1 team for this event. This makes sense, right?). If you register another team you get:

If you select the delete link for the team you get a dialog to confirm:

Confirm would remove the team tag from the runner document and the team document gets also removed.
Next: the add and remove links to update the members of a team…