The Grammarphobia Blog

Batting practice

Q: While watching baseball on TV, I repeatedly hear announcers talk about RBIs. The abbreviation “RBI” is short for “run batted in.” The plural is “runs batted in,” not “run batted ins.” So why should the abbreviated plural end with an “s”?

A: Some abbreviated phrases (such as “POW”) form the plural by adding “s” to the end (“POWs”), even though the unabbreviated phrases pluralize a principal noun that’s not at the end (“prisoners of war”).

Other abbreviations with a principal noun that’s not at the end – like “rpm” (“revolutions per minute”), “mph” (“miles per hour”), and “mpg” (“miles per gallon”) – don’t add an “s” because they’re understood as plurals already.

If in doubt about the plural of an abbreviation, check your dictionary.

As for “RBI,” it can be pluralized either way (with or without an “s” at the end), according to the new third edition of The Dickson Baseball Dictionary. But that’s just the short answer.

Dickson cites the work of the late baseball researcher Charles D. Poe, who found a confusing collection of written plurals for the abbreviation: “RBIs,” “RBI,” “rbi’s,” “RBI’s,” “R.B.I.,” “R.B.I.’s,” and “rbi.”

Merriam-Webster’s Collegiate Dictionary (11th ed.) has both “RBIs” and “RBI” as standard plurals, but it lists the “s” version as slightly more common.

I prefer “RBIs,” and that’s the plural I hear the most. But I’ll let E. J. Dione Jr. (writing in the Oct. 19, 1997, issue of the Washington Post) have the last word:

“To refer to RBIs is redundant, strictly speaking. Yet those who decline to pluralize it (‘He has 120 RBI’) sound a little strange.”

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