V for Victory

The answer to the meta-puzzle is a court contest.

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The five theme entries are all people whose last names are the same as the first parties in famous U.S. Supreme Court cases:

• 21-Across: (He's been a Bad Boy (3)) = MARTIN LAWRENCE. Lawrence v. Texas, the 2003 case striking down laws prohibiting homosexual relations.
• 29-Across: ("National Lampoon's Christmas Vacation" protagonist (4)) = CLARK GRISWOLD. Griswold v. Connecticut, the 1965 case establishing the right to birth control.
• 45-Across: (Six-term Senator from Alabama (5)) = RICHARD SHELBY. Shelby County v. Holder, the terrible 2013 case that gutted the Voting Rights Act.
• 58-Across: (Film star known for fruit hats (2)) = CARMEN MIRANDA. Miranda v. Arizona, from 1966, which established the famous "Miranda rights" for those in police custody.
• 68-Across: (Former Knick with a clothing line that's a contraction of his name (1)) = STEPHON MARBURY, with his Starbury clothing line. And that's Marbury v. Madison, the great-granddaddy of Supreme Court cases, which established the idea of judicial review back in 1803.

As suggested by the puzzle's title, "V for Victory," you should look at the "versus" for each case, namely the opposing party. Taking the initials of those opponents in the order indicated by the numbers in the clues, we get MATCH, which is indeed a type of (tennis) court contest.