So Joab’s men, along with the Cherethites, the Pelethites, and all the mighty men, marched out of Jerusalem in pursuit of Sheba son of Bichri.
We have here Amasa's fall just as he began to rise. He was nephew to David (Sa2 17:25), had been Absalom's general and commander-in-chief of his rebellious army, but, that being routed, he came over into David's interest, upon a promise that he should be general of his forces instead of Joab.
Commenting on 2 Samuel 20:4-13
And there went out after him Joab's men,.... Who though he was removed from his post as general, yet might still have the command of a regiment: and the Cherethites, and the Pelethites; over whom Benaiah was, Sa2 20:23; these attended David in his flight, and had now returned with him, Sa2 15:18, and all the mighty men; the military men that were at Jerusalem...
2Sa 20:7 Thus there went after him (Abishai) Joab’s men (the corps commanded by Joab), and the Crethi and Plethi (see at 2Sa 8:18), out of Jerusalem, to pursue Sheba.