The end of the NFL’s regular season Sunday triggered the start of two annual events: the playoffs and the period when a wave of teams fire head coaches and general managers and start frenzied searches for their replacements. The league has little control over the outcomes of the games. But over the past 20 years, the NFL has tried, and often failed, to change the composition of the highest ranks in football-related jobs at every club. For a league in which roughly 70% of NFL players are people o