1
general::
Phrase(s): pitch in (and help) (with something)
Fig. to join in and help someone with something. • Would you please pitch in and help with the party? • Come on! Pitch in!
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. Set to work vigorously, as in We pitched right in and started mowing the field. [Colloquial; second half of 1800s] 2. Join forces with others; help, cooperate. For example, We were hoping you'd pitch in and sort the books. Also see PITCH INTO.
American Heritage Idioms