A called shot is an attack, whether on a SF0 monster or SF2 mecha, that aims at one specific part of the opponent. For example, if the arm of a mecha is targeted, hit and destroyed, the equipment on that arm will no longer be of use to the pilot, but the rest of the mecha should not be harmed. (The body may still take damage from a called shot that destroys a limb, head or turret, however.) Targeting individual parts of an opponent is obviously more difficult than trying to hit the opponent entirely; a called shot involves an attack penalty of 5 for the body, and 10 for the extremities.
Called shots are most useful for getting high-quality salvage from enemy mecha. Zoanoid mecha, among others, can be disabled and captured by destroying only their heads. Battroids can also be captured by destroying their legs, immobilizing them, allowing one to pressure their pilots into ejecting. Alternatively, by destroying only the body of a mecha, one can salvage armor from the other limbs. In personal-scale combat, opponents can be killed by aiming at their heads, leaving their body armor mostly intact.
Clearly, called shots cannot be made using spread weapons, like missiles, shotguns, grenades and the Plasma Cannon. Weapons with a BV higher than one will only fire once when making a called shot; this can be used to conserve limited ammunition.