An article of footwear includes a sole assembly with a rib that is resiliently flexible, and the rib has a longitudinal axis and a transverse axis. The transverse axis extends at an acute angle relative to the ground surface, and the rib includes a first longitudinal end, a second longitudinal end, and a middle portion disposed between the first and second longitudinal ends. A height of the first and/or second longitudinal end is greater than that of the middle portion. The rib is operable to axially support a first force applied substantially along the acute angle relative to the ground surface, and the rib transverse axis remains substantially straight in response to the first force. The rib resiliently bends about the rib longitudinal axis in response to a second force applied substantially normal to the ground surface to make the rib transverse axis non-linear.