snag n.

1570s, "stump of a tree, branch," a word of Scandinavian origin; compare Old Norse snagi "clothes peg," snaga "a kind of ax," snag-hyrndr "with sharp points" ("snag-cornered"). The connecting notion seems to be "sharp protuberance, projecting point."

The general meaning, in reference to any sharp or jagged projection is recorded from 1580s; especially "tree or part of a tree in water and partly near the surface, so as to be dangerous to navigation" (1807). The figurative meaning "hidden obstacle, unexpected impediment" is from 1829.

"catch or be caught on an impediment" (intransitive), 1807, from snag (n.). Originally in American English, and often in reference to steamboats caught on branches and stumps lodged in riverbeds. Figurative use is by 1833. Of fabric, "to catch and tear on a projection," by 1854. The transitive meaning "catch, steal, pick up" is U.S. colloquial, attested from 1895. Related: Snagged; snagging.