Yes, tight hamstrings can cause severe lower back pain. When the hamstrings are excessively tight, they can alter the alignment of the pelvis, leading to an increased curvature of the lower spine. This misalignment can result in added stress on the lower back muscles and potentially compress the lumbar discs or nerves, causing severe pain. Stretching and strengthening exercises for both the hamstrings and lower back can help alleviate this discomfort and restore proper alignment, reducing the severity of pain.