How to make a team chooser?

I am making a game where the players can pick their teams, but theres a problem. All the players can just go on one team. What can I do to make the teams even and stop everyone from just joining one team.

local function countTeams( player )

	local rteam = 0
	local bteam = 0
	local neutral = 0

	for k,v in pairs(game.Players:GetChildren()) do

		if v ~= player then

			if v.Neutral then
				neutral = neutral + 1

			elseif v.TeamColor == teamRed then
				rteam = rteam + 1

			elseif v.TeamColor == teamBlue then
				bteam = bteam + 1

			else
				neutral = neutral + 1

			end
		end
	end

	return rteam, bteam, neutral

end