فَصَالُوا صَوْلَةً فِيمَنْ يَلِيهِمْ وَصُلْنَا صَوْلَةً فِيمَنْ يَلِينَا
They made their charge against those facing them, and we charged against those facing us.
Ṣālū ṣawlatan and ṣulnā ṣawlatan repeat the root Ṣ-W-L. Ṣawlatan functions as an emphatic cognate accusative (mafʿūl muṭlaq).
Fīman yalīhim and fīman yalīnā each point to the opponents directly facing one wing. The parallel charges turn the previous verse's formation into an action scene.