The native of Oshkosh, Wisconsin, threw and batted right-handed, stood 5 feet 10 inches (1.78 m) tall and weighed 190 pounds (86 kg).

In 1961, his sixth season in the Detroit farm system, he posted a 23–3 (.885) won–lost record and was selected the Most Valuable Player of the Double A Southern Association.

The performance earned Koplitz his first taste of the majors when rosters were expanded to 40 men after September 1.

In his first game in the big leagues, at Fenway Park on September 8,[1] the first batter he faced was future Baseball Hall of Famer Carl Yastrzemski, whom he struck out.

[2] Koplitz went 9–7, with two complete games, one save and a 4.21 earned run average during his MLB career.