He was nicknamed "Cool" and "The Spider", the latter because of his arms and legs, which extended to prodigious lengths when he ranged after ground balls.

Hartman's career in minor league baseball began in 1959 at the Double-A level in the Chicago Cubs' system.

He played for the Triple-A Houston Buffs in 1961 and was acquired by the expansion Colt .45s that winter before their maiden National League season.

Recalled from Triple-A in midseason 1962, he backed up regular Colt .45 shortstop Bob Lillis, starting in 42 games through the end of the year and hitting .223.

He then began 1963 on the Houston roster and appeared in 39 total games, 21 as a starting shortstop, before returning to the minors, where he played through 1967.