Simplify the following text for a Grade 9 native English-speaking person.
Original: By the early years of the twentieth century , it became common for players to wear hats with rounded tops , but some persisted with flat-topped caps , such as the Giants in 1916 , and the Pittsburgh Pirates as recently as during the 1979 World Series .
Simplified: Other teams would sometimes use the flat-topped cap , such as the Giants in 1916 , and the Pittsburgh Pirates in their 1979 World Series championship .