It's difficult question to answer.
Quote from wikipedia:"Football refers to a number of sports that involve, to varying degrees, kicking a ball with the foot to score a goal. The most popular of these sports worldwide is association football, more commonly known as just "football" or "soccer". Unqualified, the word football applies to whichever form of football is the most popular in the regional context in which the word appears, including association football, as well as American football, Australian rules football, Canadian football, Gaelic football, rugby league, rugby union, and other related games. These variations of football are known as football codes."
It's similar game but not the same way to play. some people call a game with round ball "soccer,football"; while some people called a game with oval ball "football,rugby,american football"