The Tournament

A group of the world's wealthiest and most powerful men, who are themselves tied into law enforcement agencies and criminal underworlds alike, and who also control the international media with their billions, have devised the ultimate entertainment for themselves â simply referred to as "The Tournament" â which takes place at intervals of every seven or ten years in an unspecified location, usually a large city.
"Contestants" volunteer, but due to the nature of the tournament are some of the toughest or craziest individuals on the planet â they are expected to kill, and only the last surviving combatant will win the cash prize of Â£10 million offered by William Randolph Hearst. The men and women running the tournament not only view it as entertainment, but also bet high stakes on the outcome as a huge gambling tournament, serving as the source of excitement also for the millionaires.
For each tournament, combatants are selected from the world's special forces, serial killers, athletes, trained contract killers and assassins. The last combatant standing receives not only the cash prize, but also the glory and reputation of having the title of World's Number 1, and which itself carries the legendary million-dollar-a-bullet contract killing price tag. Each of the contestants carries a tracking device, embedded under their skin, allowing the observers to monitor their movements, and the contestants to track each other. The tournament lasts twenty-four hours, and if no-one has won, then the tracking devices will explode.
The mayhem which takes place is passed off as natural disasters, terrorist outrages, accidents, or put down to rampages committed by lone madmen. The unsuspecting towns where the tournament takes place are randomly selected, and the public never know of its existence. This year, the latest tournament has come to Middlesbrough, a town in the United Kingdom â the country with the most prevalent mass surveillance in the world â so that the events of the tournament can be easily followed and recorded through the ever-present CCTV as well as satellite surveillance. They also jam the communications of the emergency services, completely taking over the electronic infrastructure, and the stage is set.
The current Tournament becomes complex due to the actions of the organisers and competitors; not only has Joshua Harlow â the winner of the last Tournament â been convinced to return because his wife was murdered and he's informed that the killer is in the Tournament, but another contestant, the Frenchman Anton Bogart, manages to remove his tracking chip, dropping it in a cup of coffee just in time for Father Joseph MacAvoy, a priest struggling with alcoholism and a crisis of faith, to drink it. With his only ally assassin Lai Lai Zhen, seeking to escape the game after her last kill, MacAvoy must race to survive before the timer runs down.
Joshua Harlow finds out in the course of the film who murdered his wife. It was Lai Lai Zhen, who had been commissioned by the organizer, Powers. Harlow blows himself and Powers into the air at the end of the film. Lai Lai Zhen and Father MacAvoy are the only survivors of the game. At the end of the film we see that Father MacAvoy is once again working as a priest and has defeated his alcohol addiction.

Question: how they select combatants?
Answer: tournament; tournament