pitch in —一起帮忙,作出贡献
最常见得意思是一起帮忙，做出贡献(to join in and help someone with something).
1.When they took up a collection for the annual dinner, he promised to pitch in.
2.Please pitch your waste paper in here.
3.As soon as the food was put on the table, all the children pitched in without waiting to be invited.