When did players start making "high salary" careers out of MLB anyways?
Not till the reserve clause was eliminated. The reserve clause bound a player to a team for life.
Later 1970s. Reggie Jackson and other Oakland A's were some of the first to jump ship for big money but even what he got is paltry compared to today.
The NFL was even later. Salaries didn't take off until early 1980s. Joe Ferguson (Bills) was the highest paid QB in 1983 and made $440,000 which is like $1.1 million today. Not chump change but not $25 million like today.