How does one use the Team Service to check to see if a certain number of players are on a team?

Like I know Team:GetPlayers() gets the list of players in a Team but if I wanted to make a Raid system for a group I need to be able to set the amount of players required per team. It doesn't seem that "if Team.Players.NumPlayers == Insert Value Here" works here. So, how would I go about doing this?

local teamA = game:GetService("Teams"):WaitForChild("Valkan")

local teamB = game:GetService("Teams"):WaitForChild("Raiders") -- Raiders

game.Players.PlayerAdded:Connect(function(a) 
if teamB:GetPlayers() >= teamA:GetPlayers() then 
    script.raid.Value = true 
    local m = Instance.new("Message",workspace) 
    m.Text = "RAID ON" 
    wait(6) 
    m:Destroy()
    end
end)