McAllister enrolled at the NCAA Division II school the University of Charleston, where he saw playing time for the Charleston Golden Eagles football team as a freshman in 2017.[4] He ran seven times for 23 yards, caught 22 passes for 193 yards and returned 13 kicks for 242 yards that season.[4][5] In 2018, he caught 20 passes for 276 yards and one touchdown and ran five times for 35 yards.[4] He was chosen first-team All-Mountain East Conference (MEC) in 2019, running for 1,119 yards and 11 touchdowns in 10 games.[6]
During the 2020–21 season, McAllister ran 36 times for 214 yards with two rushing touchdowns, also catching 15 passes for 129 yards while appearing in three games.[4] As a senior in 2021, he ran for 1,090 yards and 13 touchdowns, with an average of 7.62 yards-per-carry that ranked third nationally.[7] He led the MEC in both rushing yards and touchdowns and also totaled 32 receptions for 302 yards, having an all-purpose yards average of 142.8 per game that placed 16th at the Division II level.[7] He was named first-team All-MEC, first-team D2CCA All-Region and the MEC Offensive Player of the Year.[7][8] He ended his collegiate career with 2,561 rushing yards and 26 rushing touchdowns with an average of 7.2 yards-per-carry, along with 113 receptions for 1,047 yards and four touchdowns.[9]
After going unselected in the 2022 NFL draft, McAllister signed with the Denver Broncos as an undrafted free agent.[11] He was waived/injured on August 10 and placed on injured reserve with a hamstring injury.[9][12] He signed with the Broncos practice squad on November 22.[13] He was released from the practice squad on November 29, re-signed on December 14, and signed a reserve/future contract after the season, on January 9, 2023.[12] He was waived on May 12, 2023, re-signed on May 16, and then released on May 31.[12]
Hamilton Tiger-Cats
On June 14, 2023, McAllister signed with the Hamilton Tiger-Cats of the Canadian Football League (CFL).[14] He made the team and appeared in 16 games, being a top special teams player for the Tiger-Cats.[5][15] He totaled 13 rushes for 52 yards, 27 catches for 364 yards and two touchdowns, 41 kick returns with an average of 25.3 yards, 56 punt returns with an average of 10.8 yards, and seven missed field goal returns for 408 yards and a touchdown.[15] He was the CFL leader in kick return average and all-purpose yards.[16]
Las Vegas Raiders
Following the CFL season, McAllister signed a reserve/future contract with the Las Vegas Raiders on January 16, 2024.[17] In the team's preseason finale against the San Francisco 49ers, he returned a punt 81-yards for a touchdown and had a 35-yard touchdown reception.[18] He was waived on November 1, and re-signed to the practice squad.