Curious about this - "Place him in the back" is correct; "place him in back"
If it's speech, then is it still an error without 'the'. Are characters not allowed to speak in short sharp (grammatically incorrect) ways? If not why not?

I don't consider it acceptable because, generally, such an error comes from a non-native speaker. A native speaker is indeed likely to speak in fragments or run-ons (or plural/singular verb confusion), but an omission of an article I find unnatural. Having been in an environment where I interact with both native and non-native speakers on a daily basis, I've noticed some speech patterns. *shrugs* If you insist, by all means, keep it there. It just happens to jangle, for me.