Baseball provides many metaphors, but not many have made it to PubMed.

A ballpark is a baseball ground. Figuratively, it is a noun meaning a particular area or range, or an adjective meaning approximate. In the OED, the first recorded use of ballpark to mean the stadium was 1899, and its meaning of approximate was 1960, but there are earlier uses. It appears in PubMed as ballpark figures, ballpark estimates, ballpark approximations. The word is entirely unnecessary; an informality to suggest mateyness. A ballpark figure is a rough figure. If an estimate or an approximation is not in the ballpark then it’s pretty useless.

Some authors wrap their ballparks up in inverted commas (see previous metaphor watch), but they would be better leaving them out. “Several large series have reported incidences up to 1.2%, which is in the same ‘ballpark’ as incidences mentioned in several open series”—saying “which is about the same” is fine.

Not all PubMed’s ballparks are metaphorical, which didn’t surprise me. Large crowds gather, hence a paper in Resuscitation: “Save-a-life at the ballpark: 10-min spectator training achieves proficiency in cardiac arrest.” What did surprise me was curveball.

A curveball is something completely unexpected; the British equivalent (from cricket) is googly. There are only two googlies in PubMed, one of which provided a tantalising and completely incomprehensible abstract. This was not because of medicalese and obfuscation, but because the keywords were Einstein equations, curved space-times, non-commutative geometry, and twistor theory. The “googly problem,” apparently unresolved for nearly 40 years, “asks for a twistor description of right-handed interacting massless fields (positive helicity), using the same twistor conventions that give rise to left-handed fields (negative helicity) in the standard ‘nonlinear graviton’ and Ward constructions.” Whether the author resolved the problem, I don’t know, but as a googly breaks from the off-side, though bowled with apparent leg-break action, the term may here be rather more literal than metaphorical.

Which is what surprised me about curveball. I was expecting many metaphorical uses; and there were some, for example, “a student may be misled by a tricky question on a multiple-choice test, regardless of whether the item writer intended to ‘pitch a curveball.'” But far more were literal, because pitching curveballs is difficult and sometimes causes arm injuries.

A new ball game, often extended to a whole new ball game, indicates a completely altered situation. It’s difficult to know how altered many of PubMed’s ball games are, because they don’t always have abstracts. From one that did, and whose full text is available free, I learned that nucleic acids can be spherical, which confers new properties including the ability to cross membranes.

Neville Goodman is a retired consultant anaesthetist and a writer. He is co-author of a book on medical English.

Competing interests: I have read and understood BMJ policy on declaration of interests and declare that my only competing interest is my co-authorship of a book about medical English.