Radak: It is like "Tzukah" (Yehoshua 8:22, i.e. affliction). It can be an adjective or noun.

Radak based on Targum Yonasan: It is other afflictions (other than creditors or poverty). He leaves his house to forget his afflictions.

Malbim: His soul is internally afflicted.

Radak: It is a creditor. The Aleph is in place of a Hei. People fleeing their creditors would go to David.

Malbim: It is an external affliction.

Radak: It is poor, like "v'Yayin l'Marei Nafesh", Yishteh v'Yishkach Risho" (Mishlei 31:6, 7)

Chomas Anach: He is bitter over his Aveiros. David returned them in Teshuvah.

Malbim: It is an angry person. He risks his life on the battlefield.