I didn't have a great deal of faith in Jake Arrieta coming into the season, after he barely got his K/BB ratio above 1 last year. Arrieta showed some quality pitches, but his control was spotty and that didn't allow him to take full advantage of them. So far in 2011, he's taken a step forward in that area, and the results have been positive.
Though Arrieta's ERA is actually higher this year (4.94 to 4.66 in 2010), his FIP (4.00) is three-quarters of a run better and his xFIP (4.02) is over a full run better. A 3.6 BB/9 rate isn't fantastic, but it's certainly serviceable. He's throwing the ball in the strike-zone more often, and he's getting ahead in the count much more often; 0-1 versus 1-0 on batters 56% of the time as opposed to last year's 48% of the time.
Arrieta's also missing more bats than he did last year. A 4.7 K/9 didn't really square with his stuff, while the 7.6 K/9 he's posted thus far makes more sense*. While he's altered his usage patterns slightly - more fastballs, fewer change-ups, and a switch from the curve to the slider as his primary breaking-pitch (though he's still throwing both) - his whiff rates are up across the board:
That's a great sign, and I still think there's some room for growth - especially with the breaking-balls.
* Though maybe it's a touch higher than it "should" be, given that he's still getting swinging strikes at a below average rate. Part of the increased K's is probably his ability to get batters to two strike (due to improved control?) - 53% of batters have gone to a two-strike count against Arrieta this year (49% is the league average), compared to 43% last year.
So while I'm not quite prepared to predict a 4.00 ERA going forward or to crown Arrieta as a future ace, the 5.00 ERA I had for him before the season is looking a little high. I would like to see him get some more groundballs with this sinker - he's been a flyball pitcher thus far and has pitched up in the zone not infrequently - but I can't say I'm not very pleasantly surprised with what I've seen thus far.
Stats: ERA, FIP, xFIP, K/9 & BB/9, GB%, PitchFX