The phrase "to pick up the ball" means to take on a new responsibility, task or challenge. It is often used in sports metaphors where one teammate must step in and continue playing after another has been injured or substituted off the field. In this context, it implies that someone needs to take over an assignment or duty from another person who may no longer be able to perform it. The phrase can also be used more broadly to refer to taking on new responsibilities or stepping up in a difficult situation.