First off! Godmodding! Don't do it! It's bad, kay? Secondly... apparently being a ninja allows you to stab people with your leg?
Do ninjas replace their legs with blades? Or maybe ninja training involves sharpening your foot into a fearsome stabbing implement! I don't know!
And we never will know, because the old man never gets that far in his assault! See, Kal is a Scotsman, and Scotsmen are natural counters to ninjas! As soon as the old man spins to avoid the headbutt, Kal responds by attempting to use the fearsome counter-spinning technique of "I jump on your back and hit you repeatedly in the back of the head", a complicated maneuver in which a 6 foot plus muscular dude wearing a policewoman outfit attempts to jump on an old man's back and hit him repeatedly in the back of the head.