A paragraph break is appropriate here (so Good News Bible).

But a man named Simon, of the tribe of Benjamin, who had been made captain of the temple: The connector But doesn’t fit this context. The Greek word rendered But shifts the narrative focus to Simon. It is better to begin with “While Onias was High Priest, a man named Simon…” or “One day while Onias was High Priest, a man named Simon….” This Simon was the brother of Menelaus, who became High Priest later (see 2Macc 4.23-25). Of the tribe of Benjamin presents a problem. If Benjamin is the correct reading, the reference cannot be to the ancient tribe of Benjamin, one of the twelve tribes, since all priests had to be of the tribe of Levi. Benjamin can only then refer to one of the priestly families. Zeitlin cites rabbinic evidence that there actually was a priestly family named Benjamin. Good News Bible emends the Greek text, with some Latin and Armenian manuscripts, to read “Bilgah” (see Neh 12.5, 18). Translators may certainly follow Good News Bible here, but we prefer to say “of the Benjamin family.” Captain of the temple is well rendered by Good News Bible as “the chief administrative official of the Temple.” He probably oversaw the day-to-day management of Temple business and finances. The word captain is not a military title here. For who had been made captain of the temple, we may say “who had been made [or, they had made] an important official of the Temple.”

Had a disagreement with the high priest about the administration of the city market: Just what the disagreement was exactly about is impossible to say; it probably had something to do with the enforcement of strict Jewish law. Simon, who was perhaps a person who followed Greek culture, may have not been insistent on this. The city market would have been an open place in the central city where food was brought into the city for sale. Other goods would have been sold there also, but the disagreement between Simon and Onias probably centered around regulations concerning food. The last half of this verse may be rendered “began arguing with Onias, the high priest, over the laws regulating food in the city market.”

An alternative model for this verse is:

• One day when Onias was High Priest, a man named Simon, from the family of Benjamin, who had been made [or, whom they had made] the chief administrative officer of the Temple, began arguing with Onias about the laws regulating food in the city market.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.