Verb
(American football) To alter the position of the device, a chain holding two sticks ten yards apart, used to initially determine the position of the line crossing which yields a first down for the offense, which may be moved by penalties or by the offense gaining a first down.
(American football, by extension) To convert a play that would result in said chains being moved.
(figuratively) To advance toward a goal.
Source: en.wiktionary.org