Simplify the following text for a Grade 5 native English-speaking person.
Original: Shields has developed a style of fighting called `` American Jiu-Jitsu '' which he has tattooed on his forearm . Shields ' American Jiu-Jitsu is a no-gi style of grappling for MMA and self-defense is a complete combat art that combines the relaxed and ready position and submission techniques of Brazilian Jiu-Jitsu with the explosive takedowns , throws and transitions of world class wrestling .
Simplified: Shields holds a black belt in Brazilian Jiu-Jitsu .