Webster (http://www.merriam-webster.com/dictionary) defines weapon as:

1 : something (as a club, knife, or gun) used to injure, defeat, or destroy
2 : a means of contending against another

When an object isn't used to injure, defeat or destroy anything, such as a target rifle used outside of competition, or a ka-bar knife being used to cut firewood, is it still a weapon under this definition?

Likewise, isn't a game of chess classified as a weapon, seeing as it is a way for people to contend against eachother?

animals have violent and non-violent ways to fight out their rank. prey animals without a social structure usually compete by attractive appearance, those with a social structure have to be able to defend the herd, so their fights can be deadly. predators with a social structure fight violent because they have to be the best contender to defend against other groups or intruders of the same race. those predators without a social structure which easily could kill an opponent in such a fight, have non-violent ways. snakes with poisoned fangs tend to wrestle, biting each other would kill both and none would reproduce.

playing chess is a non social structured way of predators to compete with each other. teaching one of them or showing themselfes they are on par might be a way to prove they are worth to be friends and reliable wingmans. the game might solve stress and define which one is the first to act in critical situations. to sum up it´s not just socializing, it structures ranks and therefor is indeed a weapon ..