I have to go with CB too.
Real life example: Every February the football team I play with gets together early before conditioning begins and we all run "the hill". This hill is hell. Let me just put it that way. But it really get you jump started into conditioning drills which start mid April.
We run a particular exercise where you run up and about a 45 degrees, straight down, up at 45, straight down, up again at 45, and straight down. Three times equals one rep. While big guys like me run it forward the cornerbacks/safeties run that 45 degree up backwards (rather swiftly I might add). I tried backpedaling up the hill once and all most busted my *** something fierce.