Give velocity to a HumanRootPart when touching?

--Services
local UserInputService = game:GetService("UserInputService")
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

--Variables for Player and Mouse
local Player = Players.LocalPlayer
local Mouse = Player:GetMouse()

--Event that checks for input
UserInputService.InputBegan:Connect(function(input, proc)
    if not proc then
        if input.UserInputType == Enum.UserInputType.Keyboard and input.KeyCode == Enum.KeyCode.E then
            --Check if target is valid
            if Mouse.Target and Mouse.Target.Parent then
                local Targetted = Players:GetPlayerFromCharacter(Mouse.Target.Parent)
                if Targetted then
                    --Fire event to server, go crazy
                end
            end
        end
    end 
end)

I'm assuming you had an issue figuring out how to get a player, so I drew something up.

UIS handles input detection, and the InputBegan event gets whatever input that was initially pressed. From there you just simply need to get the mouse of the player, check if the target exists, and go from there. If you have a question about any of this let me know!