How ‘Fortnite’ Defied Convention and Became a Hit

Teenagers—and their parents—are raving about “Fortnite.” The question now is whether its creator, Epic Games Inc., can turn buzz into profits.

“Fortnite” wasn’t a big hit when it went on sale in July for $40. To attract more interest, Epic Games made an unusual decision: It created a free version alongside the paid game.

Since then, Epic Games...