Pro Football Focus (also written as ProFootballFocus, and often referred to by its initials, PFF) is a website that focuses on thorough analysis of the National Football League (NFL) and NCAA Division-I football in the United States. PFF produces 0-100 Player Grades and a range of advanced statistics for teams and players by watching, charting and grading every player on every play in every game both at the NFL and FBS level.
PFF was founded by Neil Hornsby in the United Kingdom. Dissatisfied with some limitations of standard statistics, Hornsby began grading players in 2004. The staff gradually expanded over next few years, and the site was launched in 2007. The 2006 NFL season is the first season for which PFF has complete data. For the 2011 season, PFF provided customized data to three NFL teams, agents, media and NFL players. In 2014, sports commentator and former NFL player Cris Collinsworth bought a majority interest in the service, which moved its operations to Cincinnati, near where Collinsworth lives in Ft. Thomas, Kentucky. PFF began collecting data for every NCAA Division-I college football game in 2014.
As of 2019, PFF provides customized data to all 32 NFL teams, 62 NCAA FBS teams, 4 CFL teams, national/regional media (i.e. Washington Post, The Athletic, ESPN) and sports agencies/agents.
PFF grades every NFL player on every play on a scale of -2 to +2 using half point increments. The grades are based on context and performance. A four-yard run that gains a first down after two broken tackles will receive a better grade than a four-yard run on 3rd & 5, where the ball carrier does nothing more than expected. A quarterback who makes a good pass that a receiver tips into the arms of a defender will not negatively affect the quarterback's grade on that play, despite the overall negative result for the team.
Furthermore, grades are separated by play type. Beyond just an overall grade, an offensive lineman receives one grade for pass-blocking and one for run-blocking. The average grade is meant to be zero, and raw grades are normalized.
In watching every game, PFF is also able to record information and create data that is typically unavailable. One example is how frequently individual offensive linemen yield pressure.
PFF covers every player on every play of every game at the NFL and major college football level. Such in-depth coverage of the game of football has developed and built the most comprehensive analysis of the sport in terms of player and team performance. 
By any combination of the 80-plus data points per play, 300-plus man hours per game or the 70,000-plus hours spent watching one season by its team of analysts, PFF's Signature Statistics provide detail(s) on player performance that can't be derived from traditional box-score statistics. 
PFF has been criticized by the analytics community regarding the accuracy and veracity of its ratings. In contrast to the purely quantitative ratings released by sources like Football Outsiders, TeamRankings, and numberFire, PFF uses qualitative and opinion-based grading as the root of its 0-100 Player Grades -- not its advanced statistics. As such, the 0-100 Player Grades are not truly quantitative and could be seen as being prone to bias, poor sample sizing, or other issues.