I swear that I don't enjoy torturing baseball fans. Rehashing Kerry's year might seem like that to you, but for me, it's a simple quest for understanding what went wrong.
We'll start with Kerry's basic line for 2004:
42.1 IP, 57 hits, 2 home runs allowed, 21 walks and 40 strikeouts.
Opposing batters are hitting .318 against him (for his career they have hit .235) even though his strikeout rate is higher than his career average. What is going on?
A statistical breakdown from the Hardball Times gives some clues. The defensive efficiency rating (% of balls in play turned into outs) behind him is a very low (both by team and league standards) .607. Only 15.1% of his balls in play are line drives (also low by team and league standards), and he's a neutral fly ball/ground ball pitcher who has induced an average number of popups. So, Kerry's striking out a very good number of hitters and popping up quite a few, giving up very few home runs and few line drives. Yet, the league's hitting .318 off him. That's either bad luck or bad defense, but it's not Kerry.
This year he's struggled mightily when pitching on 0 or 1 day rest. This is a reversal of his usual pattern from 2001-2003. The variance is likely due to sample size, but it could be that as he gets older, he needs a little recovery time.
What is Kerry's responsibility is his increased and unacceptably high walk rate. Otherwise, truth be told, he actually hasn't pitched that badly this year. The major issue is the number of hits he has surrendered, and this is simply not of his doing. If his confidence is not utterly destroyed by this year's experience, I think he'll be back at roughly his pre-2004 performance levels in 2005.
https://www.battersbox.ca/article.php?story=20040813023720999