Traditionally and surely incorrectly "palace guard" or the like, as if from byrh n.f. "fortress", but DJBA’s "outlaws" is probably too misleading. From the context, clearly a major socio/political group that was controlling the access to Jerusalem, almost certainly a faction of those generally referred to as the "zealots". The precise a-political connotation of the term is uncertain, but the Akkadian parallel barānû, probably an Aramaic loan there, is generally rendered "rebel". See extended discussion in AIOA p. 41.