[Kromm]

Remember also that Stamp Kick isn't a simple "stomp." It's raising your foot to about knee level and then bringing the heel down, the rear leg coming off the ground to transfer your weight onto the attacking leg as you advance into your foe. It's a kind of low Jump Kick where the jump is initiated on contact. That's how it can target the leg, not just the foot.

A simple stomp is just an ordinary kick (-2, not -3) executed against a target who's lying down.

The foot pin used in many martial arts isn't either of the above. It isn't even a strike. It's a grapple with a leg (-2 to skill, per Martial Arts, p. 79) aimed at the foot (-2 rather than -4 to hit with a grapple; see p. B370), for a net -4 to hit. You can still remove -1 for kicking the leg or foot of a standing man if using the rules on pp. 98-99 of Martial Arts. On a success, you achieve a grapple that prevents your opponent from stepping away or kicking, and that gives him -4 to DX . . . and you haven't committed hands to it, so you can use them both to strike and parry.