Yastrzemski was well known for his batting stance, holding his bat exceptionally high, giving his swing a large, dramatic arc (unexpectedly so for a well-known "fastball hitter"), and more power at the plate. In his later years, he adjusted his stance and held the bat lower. In his autobiography, he revealed that he played his last 8 years with a damaged left shoulder he kept secret, and said this injury reduced his home run power. Before that, he could hit home runs to all fields, but afterward, his home run power was mainly in pulling the ball. This is why he no longer held the bat high and used several batting stances to adjust to the injured shoulder. He explained that with each new stance, he had to change the way he swung. This is why he never came close to hitting 40 home runs again. He was also known for modifying his batting helmets by enlarging the right earhole (for comfort) and removing part of the right earflap (for better vision of the ball as it was being pitched).