Artificial turf vs. real grass: NFL's ongoing problem with playing surfaces
NFLPA expected to file grievance over Panthers' hard field turf
NFL field surface intel: Grass vs. turf, owners, problems - ESPN
Inside the NFL turf debate: Injuries, safety measures, problems - ABC7 Los Angeles
It Sucks! Angry NFL Rips Into Soldier Field's Terrible Turf
NFLPA: Field at Carolina in Week 16 maxed out the hardness scale - NBC Sports
Report: NFLPA files grievance regarding playing conditions in Lions-Panthers game, Professional
NFLPA file grievance against Panthers for turf being 'below NFL-standard'
NFLPA files grievance over hardness of stadium field
Adam Schefter] NFLPA is filing a grievance against the NFL and Carolina for the hardness of the playing field in last Saturday's Lions-Panthers game, per source. The NFLPA complained before the game