1. He fell behind in his rent, so his landlord told him to leave.
(fall behind in: to be late in making payments or the completion of work)
2.He's behind in some of his classes, so his parents found a tutor to help him.
(When a person is "behind in" a class, he or she is having trouble completing or understanding the work that is assigned.)
3. He's behind in his yardwork.
4. The jockey doesn't want to fall behind in the race.
5. Woodrow Wilson probably would have fallen behind in the election results in 1916 if he hadn't been against U.S. involvment in World War I. He changed his mind in 1917 after Germany attacked U.S. ships.