Simplify the following text for a Grade 7 native English-speaking person.
Original: On April 15 , 1997 , Robinson 's jersey number , 42 , was retired throughout Major League Baseball , the first time any jersey number had been retired throughout one of the four major American sports leagues .
Simplified: On April 15 , 1997 , Robinson 's jersey number , 42 , was retired by Major League Baseball .