I will do play the football.
Does this sentence above make sense? Then, what is the difference between
- I will play the football.
- I will do play the football.
No, this sentence does not make sense. Do-support (inserting the word do as an auxiliary verb) only occurs in the present tense (I do play football) and the simple past (I did play football), when there is no other auxiliary verb. In this case, will is the auxiliary verb, and so do cannot also be used.
When not used in a question or a negative sentence, the purpose of inserting the word do is to add emphasis to the veracity/truthfulness of the statement. This can be done with the simple future tense in speech by simply adding stress to the word will (I will play football).
Note: no article is used when using play with a sport: play football not play the football.