Killing Vamp on Metal Gear Solid 4?

Question

I know you're supposed grab him from behind but when i try that snake just feels him up turns him round and then pushes him to the floor. I am holding R1 from behind him when he gets up.

Answer 1

Keep shooting him 'til his health is 0, then (with the syringe already equipped as your item) then run up behind him and press L1 (or at least I think it's L1, and you may need to press triangle at some point? :l). From there on it's a breeze.

Hope I helped :D (I couldn't figure this out either D:)

Answer 2

Shoot him down, he will regenerate. Shoot him down again, but make sure you are really close to him. Make sure your syringe is equipped. Run up behind Vamp and CQC him (R1) and press triangle.