Do you get a reaction if you haven’t taken a turn in combat yet?

@JeremyECrawford Do you get a reaction if you haven't taken a turn in combat yet? Example A – does get a round of surprise. B – No surprise

— Ben Kirk (@benjdkirk) June 12, 2017

You can take a reaction before your first turn in combat, but not if you're surprised (see PH, 189). #DnD https://t.co/nEouvakRW9

— Jeremy Crawford (@JeremyECrawford) June 12, 2017