In this verse, as also in Psalm 140:8 and Psalm 140:11, the singular is used: deliver me, O Lord, from the evil man: preserve me from the violent man.
(Many modern translations use only the plural in this psalm). The singular makes it easier to connect this psalm to historical events in David’s life, as we know a few of David’s opponents (Saul, Absalom). That subsequently also the plural is being used, indicates that the opponents had allies. David prays in this verse for protection and liberation.
1 Au chef des chantres. Psaume de David.