Jamieson, Fausset and Brown on 1 Samuel 27:10

10. Achish said, Whither have ye made a road to-day?--that is, raid, a hostile excursion for seizing cattle and other booty.

David said, Against the south of Judah, and against the south of the Jerahmeelites--Jerahmeel was the great-grandson of Judah, and his posterity occupied the southern portion of that tribal domain.

the south of the Kenites--the posterity of Jethro, who occupied the south of Judah (Jud 1:16; Nu 24:21). The deceit practised upon his royal host and the indiscriminate slaughter committed, lest any one should escape to tell the tale, exhibit an unfavorable view of this part of David's history.