Off one's guard Meaning, Definition & Usage
- 
       adjective satellite not prepared or vigilant
       
       
 off her guard; off guard; napping; off his guard; off-guard; off your guard.
 - the blow caught him napping
- caught in an off-guard moment
- found him off his guard
 
WordNet
Definitions
- in a careless state; inattentive; unsuspicious of danger.