Chicago Cubs pitcher Jake Arrieta is having a breakthrough 2014 season. Through 18 starts with the Cubs, Arreita has a 2.80 ERA, an excellent 2.37 FIP, with a 109/23 K/BB in 103 innings with just 82 hits allowed. This is a far cry from his previous struggles in the big leagues. Is it sustainable? Let's review his development as a prospect.

Arrieta pitched college ball at Texas Christian and had an excellent 2006 season (14-4, 2.35, 111/37 K/BB in 111 innings). He was rated as a first-round talent by draft experts entering the spring of 2007, but experienced some control problems that spring (93/50 K/BB in 98 innings, 3.01 ERA) and had large bonus demands, which dropped him down to the fifth round. It took $1,100,000 for the Orioles to sign him.

Assigned to High-A Frederick for 2008, he posted a 2.87 ERA with a 120/51 K/BB in 113 innings allowing just 80 hits. He was up to 97 MPH at times and showed promise with his curve, slider, and change-up, although his command still needed polish. I had him rated as a Grade B+ prospect entering '09.

He was very effective at Double-A Bowie in '09, with a 2.59 ERA and a 70/23 K/BB in 59 innings, but his command was occasionally troublesome after he moved up to Triple-A Norfolk, raising his ERA to 3.93 with a 78/33 K/BB in 92 innings. The slider drew good reviews but his curve and change-up needed more work, though he retained a Grade B+ rating entering '10.

As you know, Arrieta spent most of '10 and '11 in the major leagues with spotty results. Although his ERA shot up to 6.20 in 2012, his component ratios actually improved dramatically, his K/9 ratio going from 4.66 in 2010 to 7.01 in 2011 to 8.66 in 2012. His walk rate went down, too, going from 4.31 in '10 to 2.75 in '12. The improved components were reflected in his FIP, which was much lower than the ERA at 4.05.

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Despite that improvement, the Orioles gave up and he was traded to the Cubs as part of a trade for Scott Feldman last year. And now here he is as one of the best pitchers in the National League.

In scouting terms, the key to Arrieta's improvement this year is greatly increased usage of his slider/cutter hybrid pitch, noted by Eno Saris back in June. Also check this video cache that Jeff Sullivan at Fangraphs put together after a dominant outing against the Red Sox back on June 30th, illustrating the "worst" pitches that Arrieta threw that day were still quite nasty. He still has the curveball, change-up, and fastball up to 95 MPH. Arm strength and stuff has never been the problem here: it was a matter of command and pitch selection.

According to Gordon Wittenmyer at the Chicago Sun-Times, Arrieta likes playing in Chicago. He is open to a long-term contract and would not demand an"astronomical" amount of money. Would it be wise for the Cubs to make an investment? Or, put in other terms, is the breakout for real?

For the most part I think this is real, yes. Although a 2.80 ERA should not be expected every year, Arrieta isn't just coming out of nowhere: he was a top prospect in both college and the minor leagues, and he was showing sabermetric signs of improvement even before he was traded.

He's never thrown 200 innings and we'll have to see what kind of workload he can handle, but Arrieta's performance surge is not just a fluke in my view.