To people who said in the IGT "I don't understand why they don't just put Fales in": I agree, you don't understand.
Yes, Clausen sucks (duh). He also was playing without the number 1 or 2 WRs against a premier defense with its pride on the line. Seattle doesn't look great but they deserve at least a little credit.
"How can Fales actually be any worse than Clausen?" is not a rhetorical question to John Fox. Coaches are paid large sums of money to have very specific answers to those kinds of questions. (Yes, they are fallible and sometimes their answers are wrong). The question Fox is actually asking himself is: "What combination of personnel, (and with what adjustments in scheme) gives us the best chance to win next week?
I guarantee he is not thinking, in week 4 of a 16 week season, that the season is over and we might as well throw our third string qb into a real game situation just to see what we might have for next year. He is also not thinking we may as well tank for a higher draft pick - that is how (some) fans think. A lot of fans were also sure Fales would be poached if he was placed on the PS instead of making the 53 last year, which says a lot about them as judges of talent.
Fox is thinking how can we score some points, get some Ws, get the season turned in a positive direction? I think the season will be further along and more obviously lost before he starts auditioning third stringers just to see what they can do in starting roles.