The writer asks this question to emphasize that he has no reason to fear when bad things happen. Alternate translation: "I have no reason to fear ... heels." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Possible meanings are 1) the writer speaks of the evil desires of his enemies as if it were a predator ready to overtake him. Alternate translation: "when the iniquity of sinful men is ready to overcome me" or 2) the writer's enemies surround him as they commit their iniquity. Alternate translation: "when my enemies surround me" (See: [[rc://en/ta/man/translate/figs-metaphor]])