A process for forming a coordination catalyst system comprising sequentially or substantially simultaneously contacting: (I) pre-catalyst reactants comprising (a) at least one first ligand-containing reactant; and (b) at least one first transition metal reactant suitable to form at least one metallocene or constrained geometry pre-catalyst compound (e.g., rac-ethylene bis(indenyl)zirconiUm dichloride); an optionally (c) at least one second ligand-containing reactant and (d) at least one second transition metal reactant suitable to form at least one non-metallocene, non-constrained geometry, bidentate or tridentate transition metal compound (e.g., tridentate 2,6-diacetylpyridine-bis(2,4,6-trimethylanaline)FeCl₂) and (II) further contacting, jointly or individually, the pre-catalyst compound(s) and optional bidentate or tridentate compound(s) with at least one support-activator agglomerate (e.g., spray dried silica/clay agglomerate). When individually contacted, the supported catalyst components can be mixed or blended. The resulting transition metal catalyst systems are suitable for addition polymerization of unsaturated monomers, e.g., ethylene and propylene.