The rule requiring National League batters to wear protective headgear went into effect in 1956, and the American League adopted a similar rule in 1958.  However, a number of players began wearing various types of head protection prior to this. Athletics infielder Lamar Newsome, for example, wore a protective insert under his cap in 1939, as shown in the clipping below. Newsome’s insert was made of tape-reinforced felt, but subsequent versions of the insert would be made of lightweight plastic and would become popular with many players.