First off it covers all professional football players, not just the NFL.
Second, the average pay of a professional football players is just over $20,000 a year (when you eliminate star quarterbacks of NFL teams).
Third, the the issue is that owners want more than the 40% of earnings they get now, after expenses.
Fourth, the players want to mitigate the increasingly dangerous and brutal aspects of the game, particularly head injuries.
Forth, the union also provides benefits, retirement and a safety nest for all former players, with a high percentage of that helping those who were seriously injured entertaining you with their dangerous work.
Most of the issue lies in the third and fifth tear, as owners say that their expenses beyond what is factored in before money is divided, have skyrocketed (stadiums, liability, negotiated television contracts, transportation and so on). Meanwhile the players association has long fought for the little guy, those players who are not in the NFL itself and those who through injuries and for other reasons are no longer playing the game.