Explanation

Step 1: Enable field security for the field
Step 2: Create a field security profile and set all the permissions for the custom attribute to Yes.
Step 3: Add TeamA to the field security profile.
Note: Field-level security is available for the default fields on most out-of-box entities, custom fields, and custom fields on custom entities. Field-level security is managed by the security profiles. To implement field-level security, a system administrator performs the following tasks.
Enable field security on one or more fields for a given entity.
Associate one more existing security profiles, or create one or more new security profiles to grant the appropriate access to specific users or teams.