out of depth

Related to out of depth: couldn't, at a loose end, clear the air, turn up, pick up on, come down to, rubbing off

out of (one's) depth

In a field or situation that exceeds one's knowledge or ability. Of course she's out of her depth with 25 employees reporting to her—she had hardly any supervisory experience before you gave her the job! I asked Alex to consult on this project because it's a bit out of my depth.
See also: depth, of, out
Farlex Dictionary of Idioms.

*out of one's depth

Fig. involved in something that is beyond one's capabilities. (*Typically: be ~; get ~.) You know, you are really out of your depth in this project. I am sure I am out of my depth in organic chemistry.
See also: depth, of, out
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • be out of (one's) depth
  • depth
  • out of (one's) depth
  • out of one's depth
  • out of your depth
  • (one's) bearings
  • at (one's) doorstep
  • at doorstep
  • at somebody's expense
  • at (one's) expense