The three-star product joins the Terps from nearby St. John's College High School.
Castleberry didn't receive a carry for Michigan last season.
Harrison suffered a season-ending knee injury against Penn State on Sept. 27.
Coach Mike Locksley has focused on building the program's foundation in his first year.
Leake and Anthony McFarland combined for 66 percent of the team's rushing yards in 2019.
The Spartans are looking to become bowl eligible, while the Terps want to finish the season on a high note.
Savoy caught six passes for 56 yards in 2019.
Fleet-Davis was held out of Saturday's game against Nebraska.
While Locksley and the Terps are out of bowl contention, they're confident in the future of the program.
“We’ve still got a lot more to prove in the two games left.”