Cop is an acronym. You can pronoun it. It's okay to pluralize acronyms. RBI is not. To prove this minor point, people say ribbies to make the abbreviation, RBI, into an acronym. Other acronyms are scuba, radar, etc.
It's only a minor point, but RBI doesn't really get an "s" on the end to make it plural. It's not an acronym.
I wasn't an English major, but I was a journalism major.
I didn't say that RBI is an acronym. I said that, through common usage, it's treated as a noun in its own right. As such, the plural form should include an 's' at the end.