a)NOT DO somethingif you get behind with a job, payments, rent etc, you do not do or pay as much of it as you should have by a particular time 〔工作、付款、房租等〕拖后;拖欠,拖延
with
I don’t want to get behind with my work.
我不想拖延工作。
You can always catch up later if you get behind.
如果你落后了,以后总是可以赶上。
b)get behind somebody informal to support someone 支持某人
The crowd really got behind them and cheered them on.