An olefin polymerization process, the process comprising: contacting a catalyst composition with an olefin monomer and optionally an olefin comonomer under polymerization conditions to produce an olefin polymer, wherein the catalyst composition comprises: (i) an activator-support comprising a solid oxide treated with an electron-withdrawing anion; and (ii) an ansa -metallocene compound having formula (I) : E(Cp A R A m )(Cp B R B n )MX q (I), wherein: M is Ti, Zr, Hf, Cr, Sc, Y, La, or a lanthanide; Cp A and Cp B independently are a cyclopentadienyl, indenyl, or fluorenyl group; each R A and R B independently is H or a hydrocarbyl, hydrocarbylsilyl, hydrocarbylamino, or hydrocarbyloxide group having up to 18 carbon atoms; E is a bridging chain of 2 to 8 silicon, germanium, or tin atoms, wherein any substituents on atoms of the bridging chain independently are H or a hydrocarbyl group having up to 18 carbon atoms; each X independently is F; Cl; Br; I; methyl; benzyl; phenyl; H; BH 4 ; OBR 2 or SO 3 R, wherein R is an alkyl or aryl group having up to 18 carbon atoms; or a hydrocarbyloxide group, a hydrocarbylamino group, or a hydrocarbylsilyl group, any of which having up to 18 carbon atoms; m is 0, 1, 2, 3, or 4; n is 0, 1, 2, 3, or 4; q is 2 when M is Ti, Zr, or Hf; and q is 1 when M is Cr, Sc, Y, La, or a lanthanide. (i) an activator-support comprising a solid oxide treated with an electron-withdrawing anion; and (ii) an ansa -metallocene compound having formula (I) : E(Cp A R A m )(Cp B R B n )MX q (I), wherein: M is Ti, Zr, Hf, Cr, Sc, Y, La, or a lanthanide; Cp A and Cp B independently are a cyclopentadienyl, indenyl, or fluorenyl group; each R A and R B independently is H or a hydrocarbyl, hydrocarbylsilyl, hydrocarbylamino, or hydrocarbyloxide group having up to 18 carbon atoms; E is a bridging chain of 2 to 8 silicon, germanium, or tin atoms, wherein any substituents on atoms of the bridging chain independently are H or a hydrocarbyl group having up to 18 carbon atoms; each X independently is F; Cl; Br; I; methyl; benzyl; phenyl; H; BH 4 ; OBR 2 or SO 3 R, wherein R is an alkyl or aryl group having up to 18 carbon atoms; or a hydrocarbyloxide group, a hydrocarbylamino group, or a hydrocarbylsilyl group, any of which having up to 18 carbon atoms; m is 0, 1, 2, 3, or 4; n is 0, 1, 2, 3, or 4; q is 2 when M is Ti, Zr, or Hf; and q is 1 when M is Cr, Sc, Y, La, or a lanthanide. M is Ti, Zr, Hf, Cr, Sc, Y, La, or a lanthanide; Cp A and Cp B independently are a cyclopentadienyl, indenyl, or fluorenyl group; each R A and R B independently is H or a hydrocarbyl, hydrocarbylsilyl, hydrocarbylamino, or hydrocarbyloxide group having up to 18 carbon atoms; E is a bridging chain of 2 to 8 silicon, germanium, or tin atoms, wherein any substituents on atoms of the bridging chain independently are H or a hydrocarbyl group having up to 18 carbon atoms; each X independently is F; Cl; Br; I; methyl; benzyl; phenyl; H; BH 4 ; OBR 2 or SO 3 R, wherein R is an alkyl or aryl group having up to 18 carbon atoms; or a hydrocarbyloxide group, a hydrocarbylamino group, or a hydrocarbylsilyl group, any of which having up to 18 carbon atoms; m is 0, 1, 2, 3, or 4; n is 0, 1, 2, 3, or 4; q is 2 when M is Ti, Zr, or Hf; and q is 1 when M is Cr, Sc, Y, La, or a lanthanide. <EOS>