וַיְמַהֵ֗ר שִׁמְעִ֤י בֶן־גֵּרָא֙ בֶּן־הַיְמִינִ֔י אֲשֶׁ֖ר מִבַּחוּרִ֑ים וַיֵּ֙רֶד֙ עִם־אִ֣ישׁ יְהוּדָ֔ה לִקְרַ֖את הַמֶּ֥לֶךְ דָּוִֽד׃
Shimei son of Gera, the Benjaminite from Bahurim, hurried down with Judah’s contingent to meet King David,
(The above rendering comes from the RJPS translation, an adaptation of the NJPS translation. Before accounting for this rendering, I will analyze the plain sense of the אִישׁ term, by employing a situation-oriented construal as outlined in “Notes on Gender in Translation,” pp. 11–16.)
This usage of אִישׁ is conventional: it profiles the referent as a distinct entity within a larger military force—for Israel’s force has consisted of Judah’s contingent plus that of the other Israelite tribes. Although they had been united in rebellion against David, the distinction between them is rapidly becoming more evident.
On the regular usage of singular אִישׁ as a “collective” term in the context of hostilities, see my comment to Judg 7:23. On its occasional use to denote a contingent of military forces, see my comment at Judg 7:24.
As for rendering into English, the NJPS ‘the Judites’ misses the collective and situational nuances. On properly rendering the collective usage of אִישׁ into idiomatic English, see my comment at Josh 10:24.