Duelling
Duelling adds 2 damage with a one-handed melee weapon when the other hand holds no weapon.
How it works
The Fighter may select Duelling as a level-one Fighting Style. Its stated damage bonus applies while wielding a melee weapon that is not Two-Handed in one hand and no weapon in the other. The supplied passage describes no activation or rest limit.
Read the supporting references
Selected Fighter fighting styles and Battle Master progression, Warlock invocations and Pact Boons, and Ranger Favoured Enemy and Natural Explorer choices. Effects and explicit conditions are drawn from the supplied passages; comparative effectiveness is not assessed. Guidance explains the referenced mechanics; it is not a tested damage ranking. Check the stated edition and source version before applying a patch-specific detail.