pitch in

verb

1. To help out; lend assistance; contribute; to do one's part to help.

   “If we all pitch in, we can raise enough money for the renovation of the church.”

   “He spent 20 minutes one afternoon describing the club he'd formed with other teenagers in his Brooklyn neighborhood. They'd each pitched in a buck a month to rent the basement of a mallet factory, which they used as a clubhouse.”

2. To begin briskly.