This idiom, from professional sports, refers to exhausting all possible efforts to win, either individually or as a team.
Figuratively, this refers to leaving one's sweat, blood, and tears on the playing field. This represents being sincere in one's effort to achieve victory, but does not refer to cheating or other morally questionable methods. It refers simply to hard work and exertion.
Example: "In football, there is no shame in being defeated as long as you leave it all on the field."