Anonymous Jeff, (the losing teammate), "losing" modifies "teammate". When the -ing has a modifying function like that, it is not a gerund, so this doesn't match your requirements. Since a gerund refers to an activity, I don't see how you can use a gerund as an appositive to a proper noun like "Jeff".
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AnonymousJeff, (the losing teammate),"losing" modifies "teammate". When the -ing has a modifying function like that, it is not a gerund, so this doesn't match your requirements.