Rapoport added Pumphrey will join Detroit's practice squad and not its active roster.
According to Garafolo, the Lions "like [Pumphrey's] potential as a returner."
The 23-year-old left San Diego State as the all-time FBS leader in rushing yards, running for 6,405 yards and 62 touchdowns in four seasons with the Aztecs.
Entering the 2017 NFL draft, Bleacher Report's Matt Miller gave Pumphrey a sixth-round grade, citing both his size (5'8" and 176 pounds) and workload (1,158 combined carries and pass receptions) as clear concerns. Miller did, however, praise Pumphrey for his "excellent vision and understanding of defensive leverage" and pass-catching ability.
Taking a flier on Pumphrey makes sense. The Lions don't need to add another running back to the 53-man roster. Detroit had Theo Riddick and Ameer Abdullah back before also signing LeGarrette Blount and using a second-round pick on Kerryon Johnson.
By putting Pumphrey on the practice squad, the Lions can get an extended look to see whether he can occupy a role either in the backfield or on the special teams unit.