i think the football concept stands for teamwork. through all their troubles, which you see them looking sad in the video or lost. then later they finally back together, they know who they are. we are one exo. like the song said, "i just want to make you love me" be us exo 12 or exo 9. i feel like its a very deep meaning to the song. and though it seems random. i dont think it really is.
i think its involves teamwork. football being a teamwork game. and idk their chemistry maybe. just guessing. they been through a lot and i guess its showing how far they came, and that they still got it.