A: What do you think of Lily?

B: She’s a great employee. Even under pressure, she’s always on the ball.

Note: The phrase means to be alert and quick to react to things competently; efficient and/or effective. This American colloquialism is believed to come from baseball, where the pitcher who puts spin or speed on the ball is apt to strike out more batters. It was being transferred to mean any kind of competence by 1912, when an article in Collier’s stated, “He’s got nothing on the ball.”