"Velocity in Professional Baseball Pitchers Passive Ranges of Motion of the Hips and Their Relationship With Pitching Biomechanics and Ball- Robb et al, AJSM 12-`10."
Not me saying that, it's the authors! Femoroacetabular dysfunction of the lead hip in baseball pitchers; causing loss of ball velocity and shoulder injury. And, it was the first article that I've seen that suggested a correlation between GIRD and hip dysfunction. The authors used fluid goniometry to assess passive AB/ADD, IR/ER of both hips (in prone by the way). Interesting they didn't assess Flex/Ext; it would have been interesting to see how they influenced the previous. A similar test was done recently by Todd Ellenbecker involving active ROM that didn't show as much of a deviation between R/L hips as passive ROM did. The authors chose passive because they felt it also measured accessory motion.
Be sure to evaluate lead hip active/passive IR on the whenever you see GIRD of the shoulder and/or elbow injury in throwers.
This is definately a case of "pattern overload" that could benefit from retro training, like doing some throwing with the opposite arm.