A quarter is another way of saying one fourth, in this setting, one fourth of a year = three months. Quarterly means something that happens every 3 months. Edit
Outfielder Ty Cobb, whose career ended in 1928, has the highest batting average in Major League Baseball (MLB) history. He batted .366 over 24 seasons, mostly with the Detroit Tigers. In addition, he won a record 11 batting titles for leading the American League in BA over the course of an entire season.
In Major League Baseball (MLB), it is calculated by dividing a player's hits by his at bats (AB). In MLB, a player in each league wins the batting title each season for having the highest batting average that year. Under current rules, a player must have 3.1 plate appearances (PA) per team game (for a total of 502 over the current 162-game season) to qualify for the batting title.