Contend, O LORD, with those who contend with me. Fight against those who fight against me.

In this Psalm David describes how he was mistreated, lied about, pursued by wicked people.

Frequently through the Psalm David will affirm his innocence- vs. 7, 7, 11, 13-14,

He calls on God to rescue him and to judge those who are mistreating him- vs. 3, 4-8, 26

He calls on God to bring the same kind of judgment upon the wicked that they are bringing upon him. We sometimes call this lex talionis. Lex talionis is literally law of the tooth. We used it to speak of how in God's justice the punishment often fits the crime.- vs. 7-8.