Charles Ellicott Commentary Psalms 140:7

"O Jehovah the Lord, the strength of my salvation, Thou hast covered my head in the day of battle." — Psalms 140:7 (ASV)

In the day of battle.— Literally, in the day of arms, that is, when he was arming for fight. God covered the warrior’s head, that is, provided the helmet of salvation (Isaiah 59:17). (Compare also Psalm 60:9: Strength of my head.) Others, however, follow the Septuagint and Authorized Version in understanding by “day of arms” the day of battle.