Very rarely do teams consummate a prospect-for-prospect swap. It seems as though GMs favor the “devil you know” over the “devil you don’t” approach, preferring to keep the young players whom they have invested time, energy and money developing.

However, the Chicago White Sox and the Texas Rangers made just such a deal in December of 2006. In a pitching prospect challenge trade, the Rangers sent former 1st rounder John Danks to the South Side as part of a deal that shipped Brandon McCarthy to Arlington. While the move was viewed as relatively even at the time, Danks has emerged as an ace-quality starter, while McCarthy has battled finger and shoulder maladies. After an inconsistent rookie season, Danks made tremendous strides in 2008:

2007: -1.62 WPA/LI, 5.50 ERA
2008: 2.99 WPA/LI, 3.32 ERA

Danks lowered his ERA by well over 2 runs this past season. Will that dramatic improvement hold? In a word, yes.

Danks upped his K rate slightly, from 7.06 in ‘07 to 7.34 in ‘08. He also slashed his walk rate significantly, from 3.5 BB/9 to 2.63 BB/9. However, the biggest difference in Danks’ numbers came in the home run department:

2007: 1.81 HR/9, 13.8 HR/FB, 34.8 GB%
2008: 0.69 HR/9, 7.4 HR/FB, 42.8 GB%

An extreme flyball pitcher in ‘07, Danks generated grounders at a much higher clip in 2008. Consequently, his home run rate dropped from untenably high to comfortably below average. He may give some of that gain back next season (his HR/FB rate was pretty low; it tends to stick around 11% for pitchers) but he should be able to limit the longball damage and avoid another 2007 fireworks spectacle, given his more even GB/FB distribution. Given the homer-happy tendencies of U.S. Cellular Field, this is no small consideration.

With a few more strikeouts, as well as significantly less walks and homers, Danks cut his FIP ERA from 5.54 in 2007 all the way down to 3.44 in 2008. To what can we attribute this dramatic turnaround? A look at Danks’ pitch data reveals the addition of a new weapon:

(FB=fastball, SL=Slider, CT=Cutter, CB=Curveball, CH=Changeup XX= unidentified. The first number is the % that the pitch was thrown, the number in parentheses is the velocity)

2007: FB 61%(89.5), SL 0.6%(81), CB 17.4%(76.9), CH 21%(81.7), XX 2.7%
2008: FB 52.2%(91.3), SL 4.7%(83.9), CT 16.4%(87.1), CB 6.4%(77) CH 20.3%(82.8), XX 4.7%

In addition to gaining nearly 2 MPH on his fastball, Danks added a cutter to his repertoire. A look at Josh Kalk’s pitch F/X data reveals why this offering is so important to Danks’ development: the cutter gives him a pitch to work away from lefties and in on the hands of right-handers. Essentially, the offering opens up a whole new quadrant of the strike zone previously unavailable to him.

Danks is no flash in the pan. Every statistical and scouting measure available points to his breakout 2008 campaign as legitimate. Don’t hesitate to invest heavily in this southpaw: he’s here to stay among the elite arms in the American League.