Warrior talent · row 3 of Protection, from level 20 (15 with Talented 5/5) · Physical

Defiance

Increases all threat generated in Defensive stance by an additional 5/10/15% while a shield is equipped.

Game files · build 1.60.1.70245Read from the WoW Forever beta client, build 1.60.1.70245.

Compared with Classic

Classic tooltip

Increases the threat generated by your attacks by 15% while in Defensive Stance.

What Blizzard said about Defiance, each line checked against the files.

Matches the files
Defiance: Now requires a shield equipped to increase threat in Defensive Stance.
The files The tooltip's Defensive Stance threat bonus (5/10/15%) works only with a shield equipped; Classic's 15% had no shield clause (spell 12792).
Defiance Class deep dives: Priest and Warrior

69876 Sep 16First beta build we archived. No changes in the client files since.