Simplify the following text for a Grade 7 native English-speaking person.
Original: Derrick Martin ( born May 16 , 1985 in St. Louis , Missouri ) is an American Football strong safety who is currently a free agent in the National Football League ( NFL ) .
Simplified: Derrick Martin ( born May 16 , 1985 in St. Louis , Missouri ) is an American football strong safety who is currently a free agent of the National Football League .