Why is "golpeara" used here?

[wrholt]

It's an old usage of the past subjunctive (or imperfect subjunctive) with the -ra endings as an equivalent of saying the modern pluperfect tense (lo) había golpeado = "had hit (him)".

In one of my advanced language courses I was taught that this usage is almost completely obsolete in modern writing EXCEPT in news reporting and some literary styles; journalists sometimes use it instead of golpeó or había golpeado for the meaning "(had) hit".

This usage is the last remnant of the original meaning of the Latin verb tense from which the past subjunctive with -ra endings evolved: in Latin the tense was the pluperfect indicative.

By comparison, the Latin verb tense from which the modern Spanish past subjunctive with -se endings evolved was the Latin past subjunctive tense.

This evolution of the Latin pluperfect to mostly merge in usage with the Latin past subjunctive into the 2 sets of endings for the Spanish/Castilian past subjunctive is specific to Spanish/Castilian. In Portuguese, for example, the equivalent forms with -ra are the simple pluperfect tense, in contrast to the Portuguese past subjunctive with -se.