off (one's) guard

Not being especially careful or vigilant; not prepared for danger or surprises; being careless or inattentive. He's got a lot of tricky moves, so don't be caught off your guard! We'll wait until he's off his guard, and then we'll take him and his company for all they're worth!

Common Names:

Name	Pronounced	Usage
Jung-Sook	jung-sook	Korean
Debby	['debi]
Bryana	-	English (Modern)
Eszter	ES-ter	Hungarian
Oluwafemi	-	Western African, Yoruba
Marcial	-	Spanish