מִן־בְּנֵי־פֶ֗רֶץ הָרֹ֛אשׁ לְכָל־שָׂרֵ֥י הַצְּבָא֖וֹת לַחֹ֥דֶשׁ הָרִאשֽׁוֹן׃
Von den Kindern Perez war er und der Häuptling aller Hauptleute des Heeres für den ersten Monat.
Rashi
the chief of all the leaders of the hosts Jashabeam was [one] of the sons of Perez, and he was the chief of all the twelve leaders, and because he was [one] of the sons of Perez, David appointed him chief.