Simplify the following text for a Grade 9 native English-speaking person.
Original: On April 18 , 1946 , Roosevelt Stadium hosted the Jersey City Giants ' season opener against the Montreal Royals , marking the professional debut of the Royals ' Jackie Robinson .
Simplified: On April 18 , 1946 , Roosevelt Stadium hosted the Jersey City Giants ' season opener against the Montreal Royals . This game was the furst professional game for the Royals ' Jackie Robinson .