blonde girl joke

Blonde girl get a job as physical trainer, First day in a new school and she's in charge of the 16 year olds game class, She watching as many of the kids are running about having fun with a ball but, One lad is stood on his own at the back of the field, she goes over and asks, " are you ok " the lad says " yes miss", so she says " why don't you go over and have fun with the ball like the others," he looks at her and says,
" its best I stay here Miss", She asks, " why is that then "
He says " I'm the goalie miss "