Dave Righetti is one of the most respected pitching coaches in the game, both by traditional and statistical measures. He's also one of the more candid coaches in the game, and if you get him on the right day, he'll open up.
Andrew Baggarly of CSN Bay Area caught him on one of those days, and asked him about Tim Lincecum:
"Now he’s got to concentrate more – pretty much the whole time he’s out there. They’re basically sitting (offspeed) when he’s not getting his fastball in a good location. And that seems to be happening at a moment’s notice with no rhyme or reason. So that tells you it doesn’t matter who’s hitting. It’s not a certain type of hitter. It can be anybody standing there at that moment when he’s lost himself a little bit and can’t get the ball where he wants to."
The whole article is worth a read, but the main point of Righetti's is that the problem is with Lincecum's head, not his arm.
"It’s never his arm," Righetti said. "In fact, his arm has never bothered him since I’ve been here. With him it’s normally a finger or a nail or he’s overworked and we try to take it easy on him. … But there’s nothing alarming or nothing I’m hiding from you."
This isn't the first time that Lincecum has struggled in his career. But it's the longest stretch of struggling he's endured so far.