Wiktionary
fall behind
vb. 1 (&lit fall behind English) 2 (context idiomatic intransitive English) To be late (for a regular event) 3 (context intransitive English) To be progressively below average in performance.
WordNet
Usage examples of "fall behind".
The third Compassionate Hand ship continued to fall behind, though it did not turn away.
He made his apologies for the violent measures of his zeal, and bade his men fall behind.
It should, then, come as little surprise that the Third World continues to fall behind the North.
And if you fall behind in your premium, your health may suffer too.
Saadhrambacoora beckoned him in, letting the flap fall behind them.