An upward spike in the player's defensive hunger as each and every pitch crosses the plate.
A coach can encourage it. But mostly it comes from within.
Most infielders act hungry as the pitch crosses. Inwardly, some are more hungry than others. The best are ravenous.
Many outfielders don't even bother to act hungry.
I was at a MLB game this spring and was blown away by the disinterested body language of the visitor's LF. Ditto regarding two OF's at a college game I attended this spring. Btw, their team was near the top of the conference standings.