What football team has the worst record?

As far as all time winning percentages go, through 15 games of the 2009 season that would be the Houston Texans who have an all time regular season record of 48-79 for a winning percentage of .378.

The Tampa Bay Buccaneers have the second lowest all time regular season winning percentage at .393 (208-322-1) and the Atlanta Falcons are third lowest at .414 (275-390-6).