I'm fifteen years late, but I've been watching The Wire, recently. In it, I noticed a particularly jarring use of the word "police" as a mass noun with finite subject. I'm a British English speaker and, to me, these are ungrammatical:

• He's good police.
• You shot police.

The second sentence is grammatical for me if it's an elision of "You shot at the police." However, "police" here refers to a single police officer and that doesn't work for me. The same goes for the first; its intended meaning is "He's a good police officer." (It's perhaps also worth noting that "good" here means more in a moral sense than in terms of ability.)

My assumption was that it's a conflict of quantification: the subject is finite, while the object isn't. However, I do allow things like:

• He's good people.
• This apple is nutritious food.

Admittedly, the first -- which is semantically close to the "police" examples -- is idiomatic, so may not conform to normal rules, and is not something one hears too many British English speakers say. However, the second one is arbitrary and seems fine to me. As such, I'm not entirely sure why I don't allow "He's good police", etc.

Regardless of that, is this usage of "police" an Americanism, a Baltimore-ism (The Wire is set in Baltimore, MD) or a police-ism (i.e., how police officers refer to themselves, localised appropriately)?