The young lions roar after their prey— Dr. Hammond observes, that lions are not provided with great swiftness of foot to pursue those beasts on which they prey. It is necessary, therefore, that this defect should be provided for some other way; and it has been affirmed, that their very roaring is useful to them for this purpose; and that when they cannot overtake their prey, they do by that fierce noise so astonish and terrify the poor beasts, that they fall down before them. This seems probable enough, and illustrates the Psalmist's expression. The prophet Amos has the same allusion, ch. Psalms 3:4. Will a lion roar in the forest, when he hath no prey? i.e. when he hath no prey in view.
Related Commentaries of Psalms 104:21
Psalms 104:21
21 The young lions roar after their prey, and seek their meat from God.