If armed with bow, Ps (O) can support eligible Bd/Sp/Pk/Ax from a 2nd or 3rd rank, if with crossbow (or sling) from a 2nd rank only.
Is there any reason ever to field Ps (O) crossbowmen over Ps (O) archers if you've got the choice? (Well, besides the fact I bought crossbowmen figs for my medieval German mercenaries.)