Simplify the following text for a Grade 10 native English-speaking person.
Original: Goals against average ( often shortened to GAA ) is a statistic used in ice hockey , water polo , lacrosse , and association football that is the mean of goals allowed per game by a goaltender .
Simplified: Goals Against Average ( GAA ) is a statistic used in ice hockey , water polo , lacrosse , and soccer that is the mean of goals allowed per game by a goaltender .