John Wesley on 2 Samuel 20:8

Amasa went - Having gathered some forces, and given due orders for the rest to follow him, he returned to Jerusalem, and by the king's command went after those mentioned ver.7, and being come up to them at the place where they waited for him, he put himself in the head of Joab's men, and the Cherethites and the Pelethites, and such as he had brought along with him, and marched before them as their general. Girded - After the manner of travellers and soldiers. Went forth - To meet and salute Amasa, who was coming towards him to do him honour. It fell - Things having (it is likely) been so contrived by Joab, that upon the least motion of his body, his sword should drop out, and he might take it up without raising Amasa's suspicion.