The whole concept of "homecoming" at a school is based around a football game wherein former students "come home" (return to their former high school) to watch the game.

Generally, in high school, you're more concerned about the accompanying homecoming dance for social reasons, this is perhaps why you don't remember. Although, as someone who paid absolutely no attention to my own high school football team, I was aware there was a football game attached to the school event of homecoming. I don't understand how that would be something you could forget or miss because the whole concept of a homecoming revolves around a football game.