Paintball (2009)

Eight strangers engaged in an intense game of experts-only paintball find their friendly game taking a terrifying turn when one member of the team begins playing by a different set of rules. It started as a remote raw battle of wits and wiles set against the backdrop of majestic wilderness. With each shot fired, the stakes grew higher. But something horrible has happened, and what was once a team sport has become a relentless struggle for individual survival. The danger growing by the minute, the combatants gradually come to realize that their greatest adversary may be the very game they set out to play.

Source: TMDb