There is provided a forming apparatus for constraining a composite charge and forming the composite charge into a highly contoured composite structure. The forming apparatus includes a first die and a second die between which the composite charge is formed. The first die has pairs of first die portions spaced apart to define a die cavity into which the composite charge is formed into a contoured hat section having a cap. The forming apparatus includes a constraining assembly having a constraining device positioned in the die cavity. The constraining device is designed to constrain a cap portion, and to apply an upward resistive force against the cap portion, and against a downward compressive force applied by the second die, to provide wrinkle prevention in the cap as the contoured hat section is formed. The constraining assembly has a retaining element to retain the constraining device.