Albert Barnes Commentary Job 41:9

"Behold, the hope of him is in vain: Will not one be cast down even at the sight of him?" — Job 41:9 (ASV)

Behold, the hope of him is in vain – That is, the hope of capturing him is futile.

Shall not one be cast down even at the sight of him? – So formidable is his appearance that the courage of anyone who would attack him is daunted, and their resolution fails. This also agrees well with the crocodile. There is perhaps scarcely any animal whose appearance would be more likely to deter someone from attacking it.