Highest level of minor-league baseball

AAA

Just below the majors, this tier is where top prospects often get their final test.

In minor-league baseball, teams are ranked by skill level from lowest to highest: Rookie, A, AA, and then AAA. The clue asks for the top tier just below the majors, which is AAA (pronounced "triple-A"). It’s a straightforward definition with no wordplay—just a direct reference to the highest minor-league classification.