The Chargers signed Grier to their active roster from New England's practice squad Monday, Tom Pelissero of NFL Network reports.
The first major move by new interim general manager JoJo Wooden comes on the heels of a Week 15 game in which Easton Stick turned the ball over three times. The Chargers are in the midst of a major shakeup going into the home stretch of the season after the departures of former general manager Tom Telesco and coach Brandon Staley, so it's not clear what the team has planned for the quarterback position for the rest of the year.