[2] As a senior, he was the Gatorade High School Football Player of the Year for Nevada after rushing for 1,491 yards on 160 carries with 19 touchdowns.

The rushing yards broke the school record held by George Jones since 1995 and was the third best total in the nation behind Melvin Gordon of Wisconsin and Tevin Coleman of Indiana.

[13][14][15] The claim was met with mixed reactions, as sportswriters questioned the validity of the record due to the NCAA's omission of bowl statistics accumulated by players prior to 2002.

[22] On March 23, 2017, he attended San Diego State's pro day, along with Damontae Kazee, Nico Siragusa, Calvin Munson, and 10 other teammates.

[23] At the conclusion of the pre-draft process, Pumphrey was projected to be a fourth or fifth round pick by the majority of NFL draft experts and scouts.

[26] He was the 12th running back selected and one of three San Diego State players chosen in the draft in 2017, along with Siragusa and Kazee.

[31] Throughout training camp, he competed against Darren Sproles, Byron Marshall, Wendell Smallwood, and Corey Clement for a role as backup running back.

[32] Head coach Doug Pederson named Pumphrey the fourth running back on the Eagles' depth chart to begin the regular season, behind LeGarrette Blount, Sproles, and Clement.

[44] On February 9, 2023, Pumphrey was hired by Sacramento State University to serve as the team's running backs coach.