fall behind (somebody/something) phrasal verb (see also fall)

1. to go more slowly than other people so that they gradually move further ahead of you:
His mother was chatting and didn’t notice that he had fallen behind.
She hurt her ankle and had fallen behind the others.

2. to become less successful than other people, companies, countries etc:
After her time in hospital, Jenny’s parents are afraid she has fallen behind educationally.
Companies that are not market-driven risk falling behind the competition.

3. to fail to finish a piece of work or pay someone money that you owe them at the right time
fall behind (somebody/something) with/on
After losing his job, he fell behind with his mortgage payments.
The project has fallen behind schedule.

[TahlilGaran] Dictionary of Contemporary English ▲

fall behind
to fail to keep up with work/studies/payments etc.
I fell behind with my homework at the beginning of the term and had problems throughout the year.

[TahlilGaran] English Idioms Dictionary ▲

fall behind
v. To go slower than others and be far behind them.
When the campers took a hike in the woods, two boys fell behind and got lost.
Frank's lessons were too hard for him, and he soon fell behind the rest of the class.
Mary was not promoted because she dreamed too much and fell behind in her lessons.

[TahlilGaran] English Idioms Dictionary ▲