Watching the first season of american ninja warrior Free Runners are the closest thing to Ninja america has. Now initially when I heard of parkour and free running it seemed it was an activity for foks that couldn't make it in gymnastics or football but it appears that that is an incorrect conception.
Free running has become so well known for producing ninja like warriors that its cousin, Parkour, it even made it in the catalog of disciplines by Crudelli in his book which catalogs nearly all known styles of martial arts. One thing is certain. Free Running just entered the mainstream.