It is not coincidence that the language used by athletes, coaches, and sports writers is laced with military rhetoric. This is because sport evolved from militaristic ideals. It is a symbolic expression of warfare. Read a bit of Norbert Elias and you'll realize that the "sportization" of warfare has turned the codification of violence into big business, which might not be such a bad thing.
Yes, two different teams compete. Yes, they use physical strength to overcome the other, but sports are nothing like war. In war, people kill each other for political, religious, economic, or territorial reasons. Sports just have competition to prove they are better and to just have fun. Ancient sports might be an exception, due to the fact that most of them involved the death of the loser, but it was for people's entertainment. War is not, nor ever was, for entertainment.