pea patch

(idiomatic) A realm of endeavor.

Example: A small piece of land planted with peas.
1952, Bernard Malamud, The Natural‎, page 170:
  Watching the way the Pirates cut up the pea patch with their merciless hitting and precision fielding, the New Yorkers grew more dejected.
1995, Murray Newton Rothbard, Making Economic Sense‎, page 158:
  It behooves any revolutionaries, educational or other, to consider all problems and consequences before they start tearing up the social pea patch.