hit a snag
Encounter a problem or obstacle. For example, We've hit a snag with this building project. The noun snag has been used in the sense of “a sharp or rough projection,” such as would impede passage, since the 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.