A hollow golf club head having face end and tail ends, a strike face at the face end, a crown, a sole of length >3.5 inches, volume 0.300 cm3, and a structural response modifying constraining member having first and second ends, the second being forward of the first and spaced from the strike face, the constraining member extending vertically and in contact with the sole and the crown at its first and second ends, and extending horizontally a maximum distance that is