Yura Khlyan

class GroupSerializer(serializers.ModelSerializer):

    user_count = serializers.SerializerMethodField()

    class Meta:
        model = Group
        fields = ('id', 'name','user_count')

    def get_user_count(self, obj):
        return obj.user_set.count()

article = form.save(commit=False)
articel.user = self.request.user
article.save()

{% for person in item.sportsmen.all %}
    {{ person.JobNameFull }}
{% endfor %}