Spell Duelist

You have specialized in the art of countering other spell casters:

• Increase your Intelligence, charisma or wisdom by 1, to a maximum of 20.
• Whenever you use your reaction to identify a spell being cast, you can cast a spell as part of the same reaction. The spell must have a casting time of 1 reaction like shield or counterspell. 

Note: This feat assumes your are playing with the rules for identifying spells from The Xanathar's Guide (i.e. arcana check using your reaction).