While at Memphis State, he turned down offers to go pro, and after only 14 college games, Hardin signed a contract with the New York Mets, which included a $10,000 bonus.

[1] On May 10, 1969, in a relief appearance, Hardin hit a game-winning walk-off home run in the bottom of the ninth inning in Baltimore's Memorial Stadium.

On July 27, 1969, Hardin starred in the Orioles' most dominant shut-out victory in their history, routing the Chicago White Sox, 17–0.

As a member of the Atlanta Braves on June 28, 1972, he hit a 2-out solo home run in the 4th inning off the Padres' Fred Norman in San Diego Stadium.

The aircraft stalled and the plane crashed while Hardin attempted to return to the airport to make an emergency landing.