_reverse_with_prefix() argument after * must be an iterable, not int

As mentioned in this comment, putting a comma at the end of the args tuple fixes it.

scores_url = reverse('get_scores', args=(obj.pk,))

(As mentioned in this SO answer, trailing comma is required for single-item tuples to disambiguate defining a tuple from an expression surrounded by parentheses)

Alternatively, as mentioned in the docs, using a list would work fine:

scores_url = reverse('get_scores', args=[obj.pk])