I was reading Erik Larsen's The Demon of Unrest and one of the things he pointed out was that, in areas of the South, blacks had to be off the streets by a given time. If they weren't, they were subject to arrest overnight (during which they might be beaten or even killed), and then "returned" to their owners the next day (where they'd likely face additional punishment).

I knew of the definition of "sundown towns" as you described them, but it seems like they're post-Civil War attempt at some kind of pseudo-slavery, combined with expanded sharecropping, "separate but equal" facilities, red-lining, voting literacy laws, etc.