napping vs off his guard

napping and off his guard both are adjectives.

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

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

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

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