The Agents Of S.H.I.E.L.D. spinoff will be lead by season 2 cast members Adrianne Palicki and Nick Blood, according to Deadline.
Palicki plays Bobbi Morse, also known as Mockingbird, a seasoned spy for S.H.I.E.L.D.. Blood plays Lance Hunter, a former British soldier and mercenary who joined Coulson's team and is also Morse's ex-husband.
The spinoff is supposed to be set up by events from this season of S.H.I.E.L.D. It is unclear whether that would involve the secret plan by Bobbi and Mack, which had been heavily teased going into the spring run of the show. - Deadline
The series will be developed by S.H.I.E.L.D. executive produer Jeffrey Bell and series writer Paul Zbyszewski. They're writing the script for the pilot and if the show goes to series Zbyszewski will serve as its showrunner.
Deadline adds that the show's setup "would allow it to air concurrently with S.H.I.E.L.D.," however, they don't expect ABC to repeat that mistake which recently happened to Once Upon A Time and Once Upon A Time In Wonderland. Deadline believes ABC could use "the spinoff as a bridge between the fall and spring portions of S.H.I.E.L.D.."