Care to re-think that one?
Why do you ask?
A tight psoas will extend the spine as to bring its origin and insertion closer together ie: increase hip flexion by changing the orientation of the spine and pelvis. This also has the effect of increasing the distance between the origin and insertion of the external rotators placing them on stretch when the leg is in neutral, thus the hip must externally rotate to achieve a resting length in the external rotators.
since the psoas is antagonistic to the glutes (among one or two other reasons i can think of) the hamstrings are forced to work harder during hip extension and are often injured as a result.
Does that clear things up for you? Or were you just looking to be argumentative? 🙂