Only show result when the author has a relation with the current user
Found out how it should be done if you can refer to an author.

My setup:


add relation ship Content : Author as "author"
add relation ship User: Group (field_group) - Appears in: user:user. with the relation to "author".
add contextual filter User: Group (field_group) - Appears in: user:user. with at "When the filter value is NOT available" -> "Provide default value" -> "PHP Code" the following code:
global $user;
$data = user_load($user-&gt;uid, TRUE);
return $data-&gt;field_group['und'][0]['nid'];