Organized team activities had originally been suspended until April 6.
Robinson served as the Terps' cornerbacks coach and defensive passing game coordinator.
The Terps are left with Josh Jackson and Lance LeGendre as their lone scholarship quarterbacks.
Pigrome played in 11 games last season, making three starts.
The Terps added two recruits to their 2021 class and one to their 2020 class.
Harrison suffered a season-ending knee injury against Penn State on Sept. 27.
Among other signings, coach Mike Locksley secured five-star wideout Rakim Jarrett.
The Terps flipped local five-star wide receiver Rakim Jarrett from LSU on Wednesday.
“He has the characteristics of the great ones,” coach Mike Locksley said.
Brooks made the All-Big Ten second team and Leake was named the return specialist of the year.