helped David. helped with David.
the band: i.e. the Amalekites, who had burned Ziklag during his absence. See 1 Samuel 30:1-20. It is assumed that we know of this.
Related Commentaries of 1 Chronicles 12:21
1 Chronicles 12:21
21 And they helped David against the band of the rovers: for they were all mighty men of valour, and were captains in the host.