FreeFalling

What is important here: If you take a look at the events of a humanoid, you'll notice that there is a freeFalling event.

The key to understanding the freeFalling event is that the argument which is given by the event is the status of whether or not the player is actually freeFalling anymore. For example, let's make a local script to test this event out:

local plr = game.Players.LocalPlayer
local chr = plr.Character or plr.CharacterAdded:wait()
local hum = chr:FindFirstChild("Humanoid")
local falling = false

    hum.FreeFalling:connect(function(isFalling)
        falling = isFalling
        if isFalling then
            while falling do
                print("Falling!")
                wait()
            end
        else
            print("Not Falling!")
        end
    end)

Now, if you want to make the character still, we obviously only have to put the humanoid WalkSpeed property to 0, which makes the player still, and if the character is not falling, then we just set the walkspeed back to normal.

local plr = game.Players.LocalPlayer
local chr = plr.Character or plr.CharacterAdded:wait()
local hum = chr:FindFirstChild("Humanoid")
local falling = false

    hum.FreeFalling:connect(function(isFalling)
        falling = isFalling
        if isFalling then
            while falling do
                hum.WalkSpeed = 0;
                wait()
            end
        else
            hum.WalkSpeed = 16;
        end
    end)

Useful Links:

Humanoid: http://wiki.roblox.com/index.php?title=API:Class/Humanoid

FreeFalling: http://wiki.roblox.com/index.php?title=API:Class/Humanoid/FreeFalling

I had a solution!, Put a script inside startercharacterscripts then put this isnide the script

local bg = script:WaitForChild("BodyVelocity")

while true do
    wait()
    if script.Parent.Humanoid.FloorMaterial == Enum.Material.Air then
        local vel = script.Parent.Humanoid.WalkSpeed
        bg.Velocity = Vector3.new((script.Parent.Humanoid.MoveDirection.X * (vel + 2)) ,0,(script.Parent.Humanoid.MoveDirection.Z * (vel + 2)))
        bg.MaxForce = Vector3.new(script.Parent.Humanoid.WalkSpeed + 100000 , 0 , script.Parent.Humanoid.WalkSpeed + 100000)
        script.Parent.Humanoid.WalkSpeed = 0
        bg.Parent = script.Parent.Torso
        repeat wait() until script.Parent.Humanoid.FloorMaterial ~= Enum.Material.Air
        script.Parent.Humanoid.WalkSpeed = vel
        bg.Parent = script
    end
end

and then, Put a body velocity parented with the script and done! It worked for me! (R6 only, Change all torso for humanoidrootpart if it is r15 or a custom rig!)

I'd recommend changing the walk speed properties or changing the controller service to "NIL".