Fifty years ago Wednesday, the official dividing line between “the way things used to be” and “the way things will be from now on” was established.

Prior to Nov. 4, 1976, the term “free agent” was a nebulous and not-so-coveted title in pro sports. Most athletes in all sports who were free agents reached that status because their previous clubs deemed them so unworthy that they couldn’t return a bag of balls if put on the market. Some of them — like Catfish Hunter two years earlier — became so because of a breached contract and a judge’s ruling.

But once arbiter Peter Seitz declared the reserve clause illegal, he did more than set the named plaintiffs — Dave McNally and Andy Messersmith — free. Suddenly, a player was eligible to flee his present team as soon as he’d played out his option.

Charley Finley acknowledges the crowd at 20th and Broadway in Oakland, Calif., Oct. 23, 1972.…