Exactly what Adam said. The only two "backups" that are having above average years are Josh McCown and Nick Foles. I will give you those two examples, but even their situations can be explained better than "rule changes". Nick Foles was drafted as a backup but with potential to start and is playing in an a Chip-Kelly offense loaded with talent. The Chicago Bears have their best WR core in team history. Marshall/Jeffery/Forte is the best WR/WR/RB pass-catching lineup in the NFL. Cutler was having the best season of his career before McCown stepped in. However, what Foles and McCown are doing is extraordinary, so I will give you those two examples.

 

The rest of your examples? Meh.

Case Keenum is 0-7 in his NFL career. His last four games he has thrown for less than 200ypg, 2 TDs, and 4 INTs. Keenum had a nice couple games, but he has not been "stellar". QB rating = 83.7. Not stellar.

 

Mike Glennon. Started 9 games this year and is yet to throw for 300 yards or more than 2 TDs in a single game. He has played well for a rookie, but he hasn't been extraordinary. Also, he was drafted to be the starter. QB rating = 86.4. Not stellar.

 

Chad Henne. On pace with career averages. Has more INTs than TDs. QB rating = 74.9. Definitely not stellar.

 

Kirk Cousins. Career 75.9 QB rating. In his only action this season he is 12 of 25 for 107 yards, 0 TDs, 2 INTs, and a fumble. Definitely not stellar.

 

Colin Kaepernick. Was drafted in the 2nd round, had a year to learn, and stepped into a great situation. I don't think Kaepernick has been "stellar". He as been good, but it definitely isn't shocking.

 

 

Now let's take a look at backup QBs who have came in this year and looked below average to terrible.

Terrelle Pryor, Matt Barkley, Scott Tolzein, Kellen Clemens, Seneca Wallace, Josh Freeman

 

 

Like Adam said, you are seeing something that is not there.

 

Regarding past years, you are wrong also. I gave you some extremely stellar performances from backups (Warner, Brady). I can go trough nearly every season and list multiple backup QBs that had better seasons than Keenum, Henne, Glennon, and Cousins.

 

For example, 2006.

Tony Romo, DAL. 19 TDs, 13 INTs. 95.1 rating.

Jeff Garcia, PHI. 10 TDs, 2 INTs. 95.8 rating.

Jay Cutler, DEN. 9 TDs, 4 INTs. 88.5 rating.

Charlie Batch, PIT. 5 TDs, 0 INTs. 121.0 rating.

Mark Brunell, WASH. 8 TDs, 4 INTs. 86.5 rating.

Kyle Boller, BAL. 5 TDs, 2 INTs. 104.0 rating.

A.J. Feely, PHI. 3 TDs, 0 INTs.

Sage Rosenfels. 3 TDs, 1 INT. 103.0 rating.

 

The idea that "backups stepping in and doing well in previous years was unheard of" is just completely wrong.

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