I'm going to make this very simple. The x-factor for the Giants is a guy that used to be a dominant force, a two-time Cy Young winner, and last year, was just a 1.5 fWAR player at age 28.
My x-factor for the San Francisco Giants in 2013 is Tim Lincecum.
After Lincecum won the Cy Young in 2008 and 2009, signs immediately began to appear that he was starting to lose his mojo. His walk has risen in each year since 2009. His strikeout rate has dropped, though it's still hovering at over a batter per inning. But last year, Lincecum's struggles came to a head. His fastball velocity was a career-worst 90.4 mph. His 2.11 strikeout to walk rate was downright disappointing, finishing tied for 71st of 88 qualified starters. He also posted far and away the highest home run rate of his career.
But there are still signs of brillance from Lincecum. Despite struggling with his command, Lincecum struck out 23% of the batters he faced, the same amount as Zack Greinke and more than teammates Matt Cain and Madison Bumgarner, as well as upper tier pitchers like Adam Wainwright, Josh Johnson, and Jake Peavy. In the second half of 2012, Lincecum got his BABIP mojo back and allowed just a .720 OPS.
Yeah, it's a bit of a copout to call a player like Tim Lincecum an x-factor. But the man had such a disappointing 2012 season, and he's been so good in the past that you have to at least entertain the option that Lincecum regains some of his previous form, be it as a starter or as a dominant, multi-inning reliever. With him approaching free agency after the season, it'll be extremely interesting to see what ends up happening with Lincecum this season.