Hi Madhulk,
It is quite possible that both "Hold nothing back" and "Leave it all on the floor" mean exactly the same thing here. They can evidently both mean "Give it everything you've got!", and perhaps the hoodlum/gangster is simply using the second of the two expressions for emphasis.
That said, it's also possible that "Leave it all on the floor!" does mean what I suggested it does in my first post above. Whatever, in either case, it's a figurative expression, not a literal one.
To be honest, the expression "Leave it all on the floor", as used here, is such a rarity in English speech as to be not worth worrying about (I have
never heard it used in British English, and maybe it's just an American thing).
In fact, you are much more likely to find the expression used in its purely literal sense in English.
For example:
Q: "Where shall I put all this shopping?"
A: "Leave it all on the floor for now!"
Hope that helps! ;-)