What is the Joe DiMaggio effect?

Joe DiMaggio was the best baseball player of his era. He was the first baseball player to earn a contract of $100,000.

Joe DiMaggio becoming the first baseball player to earn a contract worth $100,000 dollars. While the question "What took so long?" may pop into your head (he received that contract in 1949 as a 34-year-old, after all), the decision to give him that contract may not have been so obvious.