SB 12.7.14

rakṣācyutāvatārehā
 viśvasyānu yuge yuge
tiryaṅ-martyarṣi-deveṣu
 hanyante yais trayī-dviṣaḥ
Synonyms: 
rakṣā — protection; acyuta-avatāra — of the incarnations of Lord Acyuta; īhā — the activities; viśvasya — of this universe; anu yuge yuge — in each age; tiryak — among the animals; martya — human beings; ṛṣi — sages; deveṣu — and demigods; hanyante — are killed; yaiḥ — by which incarnations; trayī-dviṣaḥ — the Daityas, who are enemies of Vedic culture.
Translation: 
In each age, the infallible Lord appears in this world among the animals, human beings, sages and demigods. By His activities in these incarnations He protects the universe and kills the enemies of Vedic culture.
Purport: 

The protective activities of the Lord, indicated by the word rakṣā, constitute one of the ten fundamental topics of a Mahā-purāṇa, or a great Purāṇic literature.