Paintball, Nerf, Air Soft, fighting competitions, obstacle courses, ect., are all games where humans play at war. It was something their children even played, preparing them to be warriors in the future, no matter their adult occupations. They had plenty of competitions to show their strength, their prowess, their aggression, and their ability to take down an enemy. Often other humans. Some Vorax have the guts to challenge some humans to a game, wanting to prove to their leaders that humans are NOT as dangerous as stories make them out to be. What do the humans choose? Paintball! -- DaniAndShali
The logic was impeccable. Humans were too good at war, having practiced for most of their evolutionary timeline on their eternal enemy, the Humans. They had plenty of weapons of mass destruction that terrified even themselves. Newer, bigger, fresher, and most importantly more numerous than any previous iteration.
Some Humans were just obsessed with making more of the most powerful weapons ever created, just to have them and threaten the rest of civilisation with them. It has been theorised that, should anyone develop a weapon capable of vaporising an entire solar system from central star to oort cloud, the Humans would immediately want to possess twenty of them... and subsequently test them with absolutely no foresight whatsoever. There is another theory that Humans have already done this which explains some vast pockets of empty space where solar systems should be.
Humans can just be that scary to contemplate. Therefore this particular group of Vorax had come up with an idea. It was far from an original idea, but it was pretty creative for the Vorax. They reasoned correctly that Humans used their Deathworlder games to replace combat, and that playing such games with Humans might forge some kind of peace between two Deathworlders. Being Deathworlders themselves, the Vorax saw nothing wrong with opening the playing field to all Human games ending in the word 'ball'.