This is a standard redouble pass. First, your opponent only has 4 checkers off. Change that to 5 and its a no redouble. Second, you are threatening to close him out with any 6. Third, even if you don't close and he hits you are a favorite to hit him again when he tries to come around. Fourth, there is always a chance you can pick up another one of blacks checkers if he has an awkward roll with a one.