It is seldom discussed, but there is something unique to the football season that makes evaluation difficult. It is really short. In the NFL, each team only plays 16 games. In the NBA and NHL, there are 82 games in a season. MLB has 162. The sample size is small in football, which means front offices coaches, and analysts alike have a tricky task determining which pieces of performance are significant, and which are due to statistical noise.
Think about this. The Philadelphia Phillies were the worst team in baseball this season. They went 63-99. Between July 17 and August 4, they played 16 games. In those 16 games, they finished with a 13-3 record. Do that in the NFL, and you are a historic turnaround story. You are a team on the rise and an instant contender. For the Phillies, it was a very hot stretch for a very bad team.
Think back to the 2013 Jets. They finished the season 8-8, which was viewed as a major overachievement. They went 5-1 in games decided by a score or less. This isn't to take away from what that team accomplished winning 8 games, but it is fair to say they had some fortune along the way. In two of their games, opponents committed unforced 15 yard penalties on the second to last play of the game setting up a winning field goal. Over the course of a long 162 or even 82 game season, the good and bad breaks tend to even out. In a stretch as short as 16 games, sometimes it doesn't. Either way, with a longer season like the other leagues have, it is difficult to imagine that Jets team finishing close to .500.
This goes with players also. We all know how difficult Antonio Cromartie's 2015 has been. He has been among the least effective cornerbacks in the league in the 8 games he has played. If you play a bad 8 games in baseball, you had a rough week. Play a bad 8 games in football, and the talk is how washed up you are.
How did Matt Cassell have a season like 2010 where he threw for 27 touchdowns and 7 interceptions? Think it might have had to do with a hot stretch he was never going to be good enough to sustain? That might not tell the entire story, but I bet it is part of it.
Of course, the small sample size makes these judgments more difficult. Even though it has only been 8 games, it is entirely possible that Cromartie actually is in decline. If you have watched him, you might even argue that is likely.
When you wonder why Todd Bowles just does not bench him, do appreciate the difficultly all of us have in trying to figure out exactly how much stock we should put into small sample sizes.