John said,"I play football." doesn't this change to 

John said that he played football. Or John said that he plays football.

i can't understand?

Its in present as John said these words in the past but he does the work in present.

As  the  condition  is  in  present  tense,  the  answer  is  ,  John  said  that  he  plays  football.

John said that he plays football

it should be jhon told that he played football because play/playes changes to played.

it should be john said that he played football

no it will be john said that he is playing football.

John said that he played football

it would be 'John said that he played football'

Where did yo get this question