I would have to go back but KJ pretty much had this for years upon years. If I recall correctly KJ got a hernia from trying to pick up Oliver Miller. When they went in to repair that surgery they found a second un-diagnosed hernia that I guess didn't show up before and probably had it for years. I remember hearing an interview with the team doctor say that he thought it was the source of ongoing groin and hamstring problems plaguing him.
Have no clue if that applies to Booker but it sure sounds similar if he is having chronic hamstring issues.