A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

fall behind in something • fall behind on
 something
fall behind in something —
1
. fail to do enough of smth. and
so move to a position behind others: The country has fallen
behind its competitors in the manufacture of cheap cotton
goods. 2. fail to maintain a schedule of payments, etc.: Jacobs
began receiving letters from the bank threatening foreclosure
when he fell behind in his payments.
fall behind on something —(also: fall behind with something )
= fall behind in something 2: John fell behind on his car pay-
ments so the bank took his car back.
Note: 
The expression does not correlate in meaning with the
phrase fall back on something— turn to smth. held as a reserve
for help, etc.: They had some money in the bank to fall back on.
fall below something • fall under something
fall below something —(of a standard, etc.) fail to reach an
agreed or required level: You should identify the reasons why
your academic performance has fallen below expectations.
fall under something —
1
. (of an item) be placed in the cate-
gory mentioned: If a document falls under the physician-
patient confidentiality clause, then this section may be
withheld from public viewing. 2. (of a person) be strongly
influenced or attracted by smth.: Though she was no longer
young, she was still beautiful and John immediately fell under
her charm.
fall guy • fallen man
fall guy —
1
. a loser or victim, especially smb. who is tricked
into smth.: The president cannot be considered a “fall guy,”
since he is the commander in chief who ultimately ordered
these military adventures. 2. a person who gets blamed when
smth. goes wrong : They finally dismiss an employee in
response to the scandal. Is he just a fall guy or will more dis-
missals be forthcoming?
fallen man —
1
. (the Bible) said of man after the time when
he sinned: What is fallen man’s solution to the approach of
the Judge? He retains his pride and self-reliance and runs from
God. 2. (liter.) smb. whose behavior is against the principles
of morality: “Are you a wagering man, Dr. Waterhouse?” “I
was brought up to loathe it. But my return to London is proof
that I am a fallen man.” Cf.: fallen woman —(dated) a woman
who has lost her respectability because of extramarital sex: Sappho
runs away rather than lie to Will and trick him into marriage
with a “fallen woman.”