falling off is a noun meaning "a noticeable deterioration in performance or quality". It carries one recorded sense.
a noticeable deterioration in performance or quality
“the team went into a slump”
“a gradual slack in output”
“a drop-off in attendance”
“a falloff in quality”
Definitions, synonyms and semantic relations for falling off come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.