[1] He attended Trinidad High School and participated in football, basketball and track, winning 10 varsity letters.

[3] The Deseret News noted that "Bob is but 17 years of age, but it didn't take him long to prove that he is one of the smartest ball players seen around the Colorado Aggie field in several seasons.

[5] Four games into the season, Utah Utes coach Ike Armstrong declared Hainlen to be the best passer in the Mountain States Conference (MSC).

[7] Hainlen remained starter in 1946 and despite the team compiling a record of 2–7, he was called "the region's best passer" and was named an honorable mention all-conference selection at the end of the year.

[2][22] Hainlen was selected second-team all-conference at the end of the season, with the International News Service (INS) noting that he gave Cannon Parkinson a "run for the spot" on the first team.

[23] He was ruled ineligible to play in the 1949 season after eligibility issues due to World War II were "ironed out".

[2][25] Colorado A&M coach Julius Wagner called Hainlen "the greatest all-around athlete I've ever seen", further elaborating:[25] Last spring, Bob walked across the field where the boys were holding an intramural track meet.

[27] He spent seven weeks at the Redskins training camp but was part of a crowded quarterback room that included all-time great Sammy Baugh, Pro Bowler Harry Gilmer, and Tommy Mont.

[2][28] He was sent to the Redskins' farm team, the Wilmington Clippers of the American Football League (AFL), after not making the final roster.