So 5% is clearly made up, but let's run the numbers anyway. Let's assume the improvement diminishes linearly with number of games so 5%,4%, etc. Now you still have a backup QB so you're not looking at a 100% degradation every game for the rest of the season, let's say 50% degradation. So you're looking at about a 1% increase over the course of the season vs a 50% decrease. So if you think there's a less than 2% chance of your starter getting hurt you should do it. Looking into it quickly, in the last 3 years it looks like Bradford is the only starting QB who got seriously hurt in the preseason? So 1 out of 96, so less than 2% appears to be at least plausible.

This analysis obviously doesn't actually work for several reasons (chance of winning games doesn't scale 1 to 1 or probably even linearly with QB play for example) but my point is that without mentioning what you think the odds of a QB being hurt in the preseason are, Nick's argument is just an emotional appeal hiding behind numbers and that kind of thing annoys me even if he's right which he may well be.