From The Collaborative International Dictionary of English v.0.48 :
falloff \falloff\ n.
a noticeable decline in performance; as, a falloff in
automobile sales.
Syn: slump, drop-off, falling off.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
falloff
n 1: 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" [syn:
slump, slack, drop-off, falloff, falling off]