Esta expressão é muito utilizada no sentido figurativo, mas aqui penso que é literal, para explicar uma situação que acontecia em jogos no passado.

http://context.reverso.net/traducao/ingles-portugues/step up...
When they step up to the plate, they never strike out. Quando eles chegam à base, nunca falham um strike.

http://idioms.thefreedictionary.com/step up to the plate
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.