Established superstars such as Tom Brady or Aaron Rodgers grab all the attention when their teams do well.
But a team's success or failure can often be determined by which players make the biggest jump from year to year.
Key players such as Kansas City's Patrick Mahomes and Pittsburgh's James Conner have played major roles in their respective teams being in first place through Week 9.
And it isn't always offensive players. Of the 32 teams, nearly half (15) have featured a defensive player and one had a kicker among the most improved.
At the halfway point of this NFL season, here's a look at the most improved players for each team: