At bat
Definition 1 of 2
Pro Tip 1/3Baseball Specific
Used exclusively in the context of baseball and softball games. 
The crowd cheered as he stepped up for his first at bat.
Pro Tip 2/3Player's Turn
Refers to a player's turn facing the pitcher to try and hit the ball. 
It's Molly's turn at bat, and she's ready to score.
Pro Tip 3/3Not Literal
Doesn't mean holding a bat; it's about the chance to hit. 
With the bases loaded, his at bat could win the game.