Complex sentence: Slightly below Class A-Advanced, full season leagues like the South Atlantic League and Midwest League are a mix of players moving up from the Short-Season A and Rookie leagues, as well as the occasional experienced first-year player.
Split into simpler sentences: Slightly below Class A-Advanced, are the full season Class-A leagues, South Atlantic League and Midwest League. These leagues are a mix of players moving up from the Short-Season A and Rookie leagues, as well as the occasional experienced first-year player.