@JeremyECrawford A creature casts shocking grasp on a Mage Slayer PC. If the PC reacts to the spell being "cast," does he get his reaction?

— Easy Lee (@Easy_Lee_123) May 29, 2015

Mage Slayer doesn't specify timing, and a reaction without special timing occurs after its trigger (DMG, 252). https://t.co/tcTTpp93cZ

— Jeremy Crawford (@JeremyECrawford) May 30, 2015

@JeremyECrawford Reactions are not an "instant response," per PHB190? My group thought reactions are simultaneous based on the description.

— Easy Lee (@Easy_Lee_123) May 30, 2015

@Easy_Lee_123 Check out the Dungeon Master's Guide (p. 252), where adjudicating reactions is explained for the DM.

— Jeremy Crawford (@JeremyECrawford) May 30, 2015

@Easy_Lee_123K, then the rule in the DMG conflicts with the PHB, or the PHB is missing text that explains timing. Will this be errata’d? The PH and DMG rely on everyday English here. A response/reaction comes after something else. "Instant" means right away.

— Jeremy Crawford (@JeremyECrawford) May 31, 2015