Martinez missed his senior season because of an injury but shined during his junior year, completing 220-of-366 passes for 2,562 yards and 25 touchdowns, with just four interceptions. On the ground, Martinez ran for 1,462 yards and 14 touchdowns. Martinez also led the offense as a sophomore, throwing for better than 1,600 yards and 14 touchdowns, while also rushing for more than 900 yards.
Martinez was ranked as the No. 56 player in the ESPN300 and was the No. 4 pocket passer. Rivals and 247Sports both ranked him among the nation’s top 10 dual-threat quarterbacks, with Rivals ranking Martinez as the nation's No. 98 overall prospect and 247Sports listing him as the No. 142 overall prospect. Martinez was also selected to participate in the 2018 Under Armour High School All-America Game. He had dozens of scholarship offers and chose Nebraska over Tennessee.