If no teams volunteers, there are eight teams that the NFL can force to appear on HBO's Hard Knocks this year.

Those teams are the Baltimore Ravens, Cleveland Browns, Tennessee Titans, Indianapolis Colts, Philadelphia Eagles, Chicago Bears, Tampa Bay Buccaneers and New Orleans Saints.

A team can be forced to appear on Hard Knocks if three conditions are met: a) it hasn't appeared on Hard Knocks in the last 10 years, b) it hasn't made the playoffs in the last two years, and c) it doesn't have a new head coach.