Is it possible to track if a player is standing on a part, and when it steps off?

All you would need to do, is something like this:

Touching={}

platform.Touched:connect(function(hit)
	local Valid=true
	local player = hit.Parent
	if player.Character:FindFirstChild("RobberMatchTag") then
		local robber = player
		for i=1, #Touching do
			if Touching[i]==robber then --Checks if players already touching
				Valid=false
			end
		end
		if Valid==true then
			Touching[#Touching+1]=robber
		end
	end
end)

platform.TouchEnded:connect(function(hit) --removes players from table when they stop touching
	local player = hit.Parent
	if player.Character:FindFirstChild("RobberMatchTag") then
		local robber = player
		for i=1, #Touching do
			if Touching[i]==robber then
			Touching[i]:remove()
		end
	end
end)

I think this should work. If you have any problems please leave a comment below. Hope I helped :P