RBI, Metrodome, and Batman
As Joe Soucheray rightly complains, now Minnesota Twins announcer John Gordon and some others have decided that a batter has 23 RBI, not RBI's or RBIs. Some clown must have observed, hey, RBI stands for Runs Batted In, right? It's already plural, even for Rondell White! A higher order fool probably observed that it's valid either way, like the word sheep. The "R" in RBI can mean Run or Runs, and if I just now say RBI in all contexts, I sound more erudite!
This is too clever by half. Take the classic plural puzzler: is it Attorneys General or Attorney Generals? You can get the right answer a couple of ways. Obviously we're speaking of multiple attorneys, not multiple generals, so the first form is correct. More precisely, we pluralize the nouns, not the adjectives.
Now consider the acronym: AG. Is the plural AG? Would we say that most of the nation's AG welcomed the latest Supreme Court ruling? No, it's AG's or AGs, because AG literally stands for Attorney General, the singular form. (Some scholars prefer to reserve the apostrophe for possessive forms only.)
It's the same here. RBI is singular because there is no way to singularize "Runs Batted In" if it's plural, and it can't be both.
We've got enough problems teaching English to our children without having announcers getting them confused on something figured out correctly decades ago.