The meta answer is INVERT (Hint: Look for a 6-letter verb). The name of the puzzle was "Opposition Leaders." The 6 longest Across answers are 2-word phrases, the first of which all are opposites of other words. Rather, the "leaders" of those 6 answers are words with other words in "opposition" to them:
19A. [SUPERIOR]COURT > INFERIOR
27A. [DAY]CAMP > NIGHT
33A. [APPEAR]IN > VANISH
40A. [WEST]SIDE > EAST
45A. [LEFT]JAB > RIGHT
54A. [BOTTOM]FEEDERS > TOP
Those first words--SUPERIOR, DAY, APPEAR, WEST, LEFT and, BOTTOM--are the opposites of INFERIOR, NIGHT, VANISH, EAST, RIGHT, AND TOP.
Now what? The first letters of those words (again, "leaders") spell the word INVERT, a word alluding making something opposite, and a 6-letter verb that satisfies the puzzle's hint.