Is there a problem with this function?

When the game starts, it's supposed to team players on red, and blue and it doesn't do so. Can someone help me out? Is the function not proper?

function teams()
local balanceTeams = function(players, teams, randomize, callback)
for key = 1, #players do
local value = table.remove(players, randomize and math.random(#players) or 1);
if (not callback) or callback(key, value) then
value.TeamColor = teams[(key % (#teams + 1)) + 1];
end
end
end;

balanceTeams(
players:GetPlayers(), -- List of all players
{BrickColor.new("Bright red"), BrickColor.new("Bright blue")}, -- List of all teams
true -- Should it be random or not?
);

You should tab & space your code properly

function teams()
	local balanceTeams = function(players, teams, randomize, callback)
		for key = 1, #players do
			local value = table.remove(players, randomize and math.random(#players) or 1);
			if (not callback) or callback(key, value) then
				value.TeamColor = teams[(key % (#teams + 1)) + 1];
			end
		end
	end;

	balanceTeams(
	players:GetPlayers(), -- List of all players
	{BrickColor.new("Bright red"), BrickColor.new("Bright blue")}, -- List of all teams
	true -- Should it be random or not?
	);

You will see you are missing a final end and that teams() is never called.

There is only one more trouble with this script:

teams[(key % (#teams + 1)) + 1];

#teams + 1 should be replaced with just #teams.

When you do mod, you exclude the top value (#teams) -- however, you do include 0. So mod #teams + 1 actually allows #teams + 1 values.

(Just as the correct % #teams allows for #teams different values, [0, 1, 2, .., #teams - 1])