The phrase "sprint button" refers to a feature in video games where pressing a button makes the character run or move faster for a short period of time. Full definition
It's a shame the animation is so jerky and the game would have been served better if there was a dedicated sprint button. (gameondaily.com)
The jogging speed is definitely slower — possibly to make the new sprint button feel more effective — and I think they've dropped it too much. (ps3attitude.com)
Under controls, Automatic Sprint, allows for sprinting without pressing an additional sprint button. (dagersystem.com)