1.Lit. [for a batter in baseball] to move near home plate in preparation for striking the ball when it is pitched. The batter stepped up to the plate and glared at the pitcher.
2.Fig. to move into a position where one is ready to do a task. It's time for Tom to step up to the plate and take on his share of work.
phr. to voluntarily assume responsibility for something. (From baseball, referring to a batter approaching home plate.) The company stepped up to the plate and paid for the time and effort I spent repairing the unit.