This is a baseball term that refers to how events are recorded in the scorecard. For every batter who comes to bat, there is a frame in the scorecard. Each frame tracks what occurs during and after the at bat. Every type of event has an abbreviation or notation so it can be easily marked on a piece of paper containing many frames. The term "frame" is used because each frame is a small square or rectangle on the printed page.
A typical score sheet will have nine frames per inning, which allows for plenty of space to record the action during a given inning. Within each frame, the scorekeeper may mark many things, such as pitch count when the ball was hit, where it was hit, what base the batter advanced to, if any runs scored, etc. In the modern age of baseball, physical scorecards are used infrequently, but the idea of a frame persists in its digital representations.