1. move slower or make less progress than others, fail to remain as current as one should with something
fall behind someone/schedule
Fall behind is a phrasal verb with a number of meanings. To fall behind a group or other people means to move more slowly than others so that you end up in a position behind them. To fall behind in something can also mean to fail to make progress on a par with others or to be less successful than others in the same activity or field. To fall behind can also mean to fail to do something on the time that was agreed. You can fall behind on your rent if you don't pay on time, for example, or a fall behind in your schoolwork.