Radak: It has a full Kamatz; it is a command, like "Shamrah Zos l'Olam" (Divrei ha'Yamim I, 29:18), "Zachrah Li Elokai l'Tovah" (Nechemyah 13:31). There, it is a Kamatz Chataf (with a Sheva), like is proper; here it is a full Kamatz to beautify the song. The same applies to "Shamreni Kel Ki Chasisi Vach" (above, 16:1).

Rashi citing Shocher Tov: I hear people revile and insult me, and I could take vengeance, but I am silent. Radak - such a person may call himself a Chasid.

Rashi (citing Brachos 4a): Other kings sit amidst grandeur, and my hands are dirty with blood, Shefir (the outer skin of an aborted fetus) and Shilya (fetal sac, to see if a woman is Tehorah, and permitted to her husband) ¹ .

Brachos 4a: Other kings sleep until three hours of the day, and I rise at midnight to praise You.

Radak: He was a Chasid (went beyond the letter of the law) with Elokim and with people. Even though he sinned sometimes, his heart was straight and he regretted his sin. He glorified himself (that he is a Chasid) only against his enemies who did evil to him, and he did not do evil to them, rather, he benefited them. They rejoiced over his downfall, and he rejoiced over their good - "va'Achaltzah Tzorerai Reikam" (7:5), "Nasata Simchah v'Libi me'Es Deganam v'Sirosham Rabu" (4:8). Also Sha'ul pursued him, and he saved him twice. He was a Chasid also with his other enemies.

Malbim: "Im Chasid Tischasad" (18:26). Guard me, lest I falter from Chasidus due to pursuit of my enemies.

Radak: It is as if it says Atah Elokai, save Your servant who trusts in You. 'El' is used with Bitachon in place of the prefix Beis, like "Betach El Hashem b'Chol Libecha" (Mishlei 3:5); sometimes El is like the prefix Beis. "V'El ha'Aron Titen Es ha'Edus" (Shemos 25:21) is like uva'Aron.

Malbim: Since I trust in You, You should save me, for the honor of Your name, to help those who trust in You.