Hello!
Spears can be wielded by Small Stature creatures (like halflings and gnomes) as a two-handed weapon.
For the purposes of Parry AC, they are treated like a regular 2-hander, applying 1 point of AC per 10 points of Parry.
Given that the spear is effectively a pike in the hands of a halfling or gnome, is it an oversight that it is not treated like a polearm (halberd) in the hands of a medium creature, granting 1 point of AC per 5 ranks, not 10?