The NFL is a 9 billion dollar per year money making machine, yet it is the only one of the four major team sports to have part time officials. I realize that the other three are in action throughout the week, and football is primarily a weekend thing, but part timers, in my opinion, result in wild inconsistency in officiating from crew to crew, and from officials within each crew.
Make these guys full time. Bring them to a central location each week, review the recent games, study film of upcoming teams, do some conditioning work, and get a single focused message from the league's supervisor of officials, reinforced in person, weekly.
Of course it will never happen, because after making money what the NFL likes to do most is keep money.