Today David Price will square off against the 25 year old lefty Felix Doubront. Doubront was was a decent but not great prospect when he was in the minors. After the 2010 season Baseball America ranked him the number five prospect in the Boston system. There was some question at the time whether his future lay as a starter or reliever, but with strong performances last year and this year, he's firmly entrenched himself in the Red Sox rotation.
Doubront's fastball and sinker also sit in the low to mid 90s, but his cut fastball is a tad slower than Lester's, in the mid 80s. The biggest difference is Doubront's 75 mph curve which, in contrast to Lester's sweeper, has true 12-6 motion and great depth.
Take a look at Doubront's stats as a starter, courtesy of FanGraphs.
So this year it seems like Doubront might be pretty good, but last year it seemed like maybe he wasn't. Mostly his stats are the same. In 2013, his strikeouts are down a bit, but so are his walks. The real difference is the disagreement between his ERA/FIP and his xFIP. It's all in the HR/FB.
With the help of the Brooks Baseball player cards, it's easy to see what's gone differently. In 2012, Doubront gave up a HR/(FB+LD) of 10% or more on every pitch except for his curve (against which hitters hit no home runs) In 2013, hitters haven't been able to tag any of his secondary offerings. What home runs he has given up have only come against the hard stuff.
Keep in mind, the league average for HR/FB is somewhere around 12%. With the young lefty not having had time to establish a reliable career average, I'm going to go ahead and stick with xFIP on this one, which thinks of Felix Doubront as a good but not great starting pitcher.