[Answered ]-Django invalid literal for int() with base 10: 'Stalone'

You need to put inside value="{{ user.jucator }}" the actual id of the jucator object. Not the jucator object itself.

So, change to this: value="{{ user.jucator.id }}". Now you can query with Player.objects.filter(jucator__in=list_of_checks) since list_of_checks containts a list of integers (the ids of jucators).