off base

Short definition from Wiktionary

Prepositional phrase

1. 1
   Situated or happening outside the boundaries of a military base.
2. 2
   Positioned somewhere between the bases, and hence vulnerable to being caught out.
3. 3
   Mistaken; misguided; somewhat wrong in opinion or judgment.
4. 4
   Incorrect or inappropriate; not properly executed, envisioned, or understood.

Adjective

1. 1
   Alternative form of off base.