Can a compressed sciatic nerve cause leg weakness? Specifically the hamstring?

Possibly. A compressed sciatic nerve can cause leg weakness. Often pain down the leg is due to a lumbar radiculopathy or irritation to the lumbar nerve roots that make up the sciatic nerve. The distribution of pain depends on which nerve is irritated although pain in the back or leg or "hamstring" is common. See your md if this pain lasts greater than 2 weeks.