Question

didn't he play a good football? Change to assertive and question tag

Answer 1

He plays good football. Does’nt he?

This is an assertive statement and at the same time there is a question tag associated with it.

This seems to the most appropriate answer to the corresponding question.

For further information about the use of grammar, sentence construction, visit relevant resources available online.

Answer 2

He plays a good football is the assertive answer for the question.

Question tags are generally used to reassure or confirm the things that  we have said.

That is, the speaker himself knows the fact we are doing so, but he tries to confirm or reassure the fact by adding a question tag.