Inazuma Eleven got kind of violent for a kid's show standards. It's starts with kids playing football (soccer for you gajin bakas) but whenever they have to play against a team that is presented as the villains of the current arc, shit gets pretty rough and opposing players intentionally injure the main characters by kicking the ball at them.
There was an arc where aliens show up because they wanted to destroy earth but they concluded that it wouldn't be interesting to do so with weapons because their technology was much more advanced than that of earth so instead, they wanted to destroy it with something that humans created themselves thus they chose football matches. There's another arc where they play against a team that uses doping to attain god-like powers, keep in mind that this match was part of a highschool tournament and the players were all underage.