NET
13 Now Jeroboam had sent some men to ambush the Judahite army from behind. The main army was in front of the Judahite army; the ambushers were behind it.
Darby
13 But Jeroboam caused an ambush to come about behind them; and they were before Judah, and the ambush behind them.
KJV
13 But Jeroboam caused an ambushment to come about behind them: so they were before Judah, and the ambushment [was] behind them.