"Contend, LORD, with those who contend with me" (35:1). Is it right to ask God to take my side?

The psalm asks for more than a side. It asks for a judgment, and says whose righteousness it rests on: "Vindicate me, LORD my God, according to your righteousness" (35:24) (tap righteousness). Vindicate is shafat, which Brown-Driver-Briggs gives as "judge, govern", and among its senses "decide controversy". The psalmist gives his grounds: his enemies act "without cause" (35:7), they are "my enemies wrongfully" and "hate me without a cause" (35:19), and "They reward me evil for good" (35:12). Then he leaves the verdict with the LORD. He asks for others to see it: "Let those who favor my righteous cause shout for joy and be glad" (35:27), where my righteous cause is tsedeq, the word of righteousness in 35:24 and 35:28, with my joined to it. And the psalm ends on the LORD's righteousness, not his own: "My tongue shall talk about your righteousness" (35:28). The psalm doesn't say more than that about whether the psalmist was without fault; the chapters on Psalms 7, 17 and 26 take up that question.