Derrick most likely has a lumbar strain with no evidence of cauda equina. In general the management depends on the history and past medical history.
First of all rule out any red flags for derrick – ask about bladder and bowel control, any symptoms of nerve impingement eg pins and needles, numbness. If so arrange emergency hospital admission. Also arrange admission if you suspect any serious underlying causes.
It looks like acute non-specific low back pain.
Document how you are managing Derrick remembering to include the following points;
Reassess Derrick especially if he has new symptoms. Assess if he is adhering to the advice you initially gave him. If he has chronic low back pain then a physical and psychological approach is recommended.