In both stories, an oppressive government forces a group of selected teenagers and adolescents to fight to the death. Although they have some differences, there’s no denying the central similarities. The similarities are difficult to ignore. Both involve children who are picked at random to take part in a death match. Participants are given bags or shown places containing random weapons. The tyrannical government ships them off to a remote location, where they are told to kill and fight for survival.
Why repeat what everyone else has said? They have the exact same premise. Which admittedly is about as original as the wheel. The argument about both books being different rings hollow. It's like claiming that because dialogue and actors are different in an American remake that makes it an entirely different movie. Well it isn't and you have court rulings to support that
Lets put both of them together, Hunger Games takes people from different sections and put them in a battle to the death and the last one living is the winner. Battle Royale takes an entire classroom and puts them on an island till one is left and the rest are dead. It is an exact rip off except where they get the people from, but they did make it interesting and its American which is why it was popular.
Many movies have similar story lines, but the distinctions between the hunger games and battle royale make them two separate movies, not their similarities. If you had read the books you would know how distinct they are from one another,and you would probably compare them both to "the running man." One key difference is the purpose of the games. In BR, they are illegal and for the purpose of entertainment. In HG they are sanctioned by the government and used as a means for control. If you go just on that, HG is more of a rip off from "Death Race".
The Hunger Games show why these children are sent into these tournaments in deeper and more thought provoking way than Battle Royale was. BR is a lesson to kids who disrespect their elders. THG is about the divisive states and classes, the rich and poor. It's about control and suppression in the name of entertainment. What I prefer about The Hunger Games is that the story is meatier and more complex. It's about uprising against state control, than simply surviving a gladiatorial deathmatch. Battle Royale is great for the action and gore but the story in Hunger Games goes far deeper I think. It questions how society can become, even with the pageants made of children who become celebrities for extra support in the death arena.
However, it's in the focus of the story that the difference lies. While they are both about a tyrannical government sending youths to murder each other, Battle Royale really sticks to it. I'm not going to be one of those people who tries to deny that the games themselves don't rip off battle royale, because they completely do. But Hunger Games has elements besides political and social commentary, because it's the first part of a trilogy, the hunger games are just a plot device, unlike in Battle Royale where it's the main thing. In Catching Fire it's all about both the build up to mockingjay & the political structure of panem. And Mockingjay is entirely about the revolution, the games don't even remotely come up.
They may have a similar plot device, but all in all they are very different books.