Hamner was one of the key players on the "Whiz Kids", the 1950 National League (NL) champion Philadelphia Phillies.

A right-handed hitting shortstop with moderate power, Hamner compiled more than 80 runs batted in (RBI) four times.

Hamner then became a Kansas City Athletics’ Minor League Baseball (MiLB), manager, reappearing briefly with the A's as a pitcher during the 1962 season.

In 17 major league seasons, Hamner compiled a .262 batting average with 104 home runs.

As a pitcher, he was winless with two losses, with an earned run average (ERA) of 5.40, in seven games, and 13+1⁄3 innings pitched.