Offensive wasn't what I was thinking. Unworkable was more in my mind if it were realistic.

No sanitation, no food, and no water. You can't drink blood (you'll just vomit it back up), and cannibalism is a big taboo in most societies so no one will be around long enough to consider it as a food source anyway. And for any organised practice of it, there is no accompanying ritual or preparation to make it more "palatable". And then there's a 20 foot drop on to hard stone to "get in" which will probably lead to a nice complicated fracture or two.

You average prisoner's life expectancy is three days. And the only thing the people from the galleries will be seeing is a bunch of dehydrated injured people sat around in dirty and smelly conditions. There won't be any "pit fighting". =P