Sources:

http://www.graphicmania.net/40-special-moments-collection-of-sports-photography/

http://indulgy.com/post/uO2AL247i1/street-spirit

http://photography-on-the.net/forum/showthread.php?t=283306

https://500px.com/photo/25171533/race-by-j%C3%B6rgen-ekstrand

https://www.behance.net/gallery/Climbing-Rocks/422641

http://adventure.nationalgeographic.com/adventure/extreme-photo-of-the-week/

http://www.buzzfeed.com/peggy/these-photos-will-make-your-stomach-drop?sub=2167995_1115163#.fi10K4WKq