Why does my left foot drop when I walk?

Many causes. There are many causes for foot drop, including brain injury, spinal cord damage, pinched nerve in the back, pinched nerve at the knee, disruption of the nerve-muscle junction, or muscle damage. A neurologist can help to narrow down possible causes and guide further treatment.
"Foot Drop" If you haven't had this checked, you really need to. The nerves to your shin muscles may be weak. This can be due to a significant nerve problem -- possibly from a pinched nerve in your back. Best treated early to avoid worse problems!

Related Questions

Fell at work onto buttucks, walk with a limp, left foot drop, and constant pain on the left side all the way down from my back to my leg, pain moving?

Urgent matter. Any injury resulting in a loss of function is an urgent matter for medical attention. Foot drop due to an acute nerve injury can become permanent. Seek emergency care to assess your lumbar/sacral spine and the degree of injury causing your foot drop now! Read more...
Wit a neurologic . deficit like a foot drop I would recommend first seeing your own doctor for initial screening and imaging studies. May be a temporary problem but may not . Don't wait very long. Read more...