OK, so this isn't exactly "Hard Knocks," but here's a video about the New York Jets and their offseason MMA training with Martin Rooney is still pretty interesting.
There are some commonalities between mixed martial arts and football, mainly in the hand-to-hand aspect. Being on the offensive or defensive lines isn't much different that working for leverage in the clinch during an MMA fight.
Just ask Jared Allen, the Minnesota VIkings defensive end. He worked with Jay Glazer of MMAAthletics.tv (and Fox Sports) starting before the 2007 season and has totaled 44.5 sacks in three seasons. Compare that with his 27.5 sacks the three previous seasons.