What is wrong with my script?

local c = game.Players:GetChildren() 
local r = math.random(1,game.Players.NumPlayers)
local hum = plr.Character:WaitForChild("Humanoid") 
RANDOMPERSON = nil 
for i = 1,#c do 
if i == r then 
RANDOMPERSON = c[i]
sword = game.Lighting.Sword5:Clone()
sword.Parent = RANDOMPERSON.Backpack
hum.WalkSpeed = 22
hum.Health = 250
end
end

I got an error saying

Workspace.Map_Changer:93: attempt to index global 'plr' (a nil value)

plr = game.Players:WaitForChild("Character").Parent.Character.Humanoid

not

c = game.Players:GetChildreen()

but

plr = game.Players:GetPlayers()

or if u do c = game.Players:GetPlayers, then instead of typing plr use c cos u didn't define plr...