Quite easy:
local teamBlue = createTeam ( "Team Blue", 0, 0, 255 )
local teamRed = createTeam ( "Team Red", 255, 0, 0 )
local teams = {teamBlue,teamRed}
local randomteam = teams[math.random(#teams)]
function setTeams()
for _, player in ipairs(getElementsByType("player")) do -- We are going to launch the script for every single player.
setPlayerTeam(player, randomteam)
end
end
addEventHandler("onResourceStart", getRootElement(), setTeams)