off-guard vs off his guard

off-guard and off his guard both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off-guard	No	Yes	No	No
off his guard	No	Yes	No	No

As adjectives, off-guard and off his guard are synonyms defined as:

Other synonyms of off-guard include napping, off guard, off her guard, off one's guard, off your guard.

off-guard (adjective)	off his guard (adjective)
not prepared or vigilant	not prepared or vigilant