AaronGleeman.com

Earlier this week I discussed the importance of putting minor-league performances in proper context and introduced a system that attempts to do that by accounting and adjusting for factors like leagues, ballparks, run-scoring environments, ages, and defensive positions. I then used that same system to examine the Twins' minor-league hitters, producing a context-adjusted hitting line for each player and determining which prospects had the best offensive seasons in 2007.

If you missed either of those two entries you'll want to go back and read them, because today I'll be using the same system to examine the Twins' minor-league pitchers. Evaluating pitchers is more difficult than evaluating hitters, because pitchers rely heavily on the defense behind them. Beyond that, pitchers often exit games with runners on base and whether or not those runners score off the pitcher who comes in from the bullpen can have a big impact on ERAs and win-loss records.

All of which is why, rather than looking at more traditional stats, I'm instead focusing on a metric called FIP, which is short for Fielding Independent Pitching. Designed to look like ERA--the MLB average was right around 4.50--FIP measures only things that a pitcher is specifically responsible for, including strikeouts, walks, and home runs. The idea is to remove the impact of the defense behind them, the pitchers who relieve them, and any luck involved.

After calculating FIPs for each of the Twins' minor-league pitchers, I then adjusted them based on the run-scoring environments that they played in. The Twins' minor-league system is filled with extremely pitcher-friendly environments, which makes hitting prospects look worse and pitching prospects look better. In both cases the result is misleading numbers, but by accounting for that and normalizing run-scoring environments to fit the level of offense found in MLB, it paints a clearer picture.

Basically, the adjustments put everyone on an even playing field before evaluating their performance. A tremendous number of Twins minor leaguers posted ERAs in the 3.00s and 4.00s this year, but many of them did so while being below average at preventing runs because their league was such a low run-scoring environment. MLB as a whole had a 4.47 ERA in 2007, while the four full-season leagues in the Twins' minor-league system had ERAs of 3.98, 4.19, 3.96, and 3.78.

You're bound to post nice-looking ERAs when offense is 10-15 percent below MLB, which is why run-scoring adjustments are important. Once that's complete, I made further adjustments for how old each pitcher was relative to the prospects that he was competing against. Age is an important and often overlooked factor in projecting prospect development, and in most cases a 4.00 ERA from a 22-year-old at Double-A is a lot more impressive than a 3.50 ERA from a 28-year-old at Triple-A.

Before I get to the numbers, please note that these are not my rankings of the Twins' top prospects. That annual list will be published later this offseason and includes both multi-year track records and long-term potential as huge factors, whereas the numbers below focus solely on what each player did this year. The point here is to simply determine who had the best 2007 season by putting everyone's numbers through the same context-adjusting system.

100+ INNINGS        FIP     70-99 INNINGS       FIP     40-69 INNINGS       FIP
Kevin Slowey       2.40     Robert Delaney     2.37     Bradley Tippett    1.64
Tyler Robertson    2.48     Matt Garza         2.86     Michael Tarsi      2.40
Anthony Swarzak    3.13     Eduardo Morlan     2.94     Michael McCardell  2.43
Yohan Pino         3.49     Joshua Hill        3.85     Spencer Steedley   2.69
Oswaldo Sosa       3.53     Armando Gabino     4.07     Scott Baker        2.75
Ryan Mullins       3.53     Julio DePaula      4.13     Liam Hendriks      2.75
Jay Rainville      3.64     Jay Sawatski       4.14     Michael Allen      3.55
Jeffrey Manship    3.65     Bobby Korecky      4.18     Errol Simonitsch   3.61
Alex Burnett       3.68     Dan Leatherman     4.53     Aaron Craig        3.75
Zachary Ward       3.71     Danny Vais         4.59     Carmen Cali        3.93
Brian Bass         3.72     Daniel Powers      4.71     David Bromber      3.96
Nick Blackburn     3.74     J.P. Martinez      4.71     Brian Forystek     4.44
Brian Duensing     3.88     Kyle Aselton       4.93     Daniel Berland     4.48
Kyle Waldrop       3.95     Brian Kirwan       5.04     Frank Mata         4.70
Adam Hawes         5.18     Timothy Lahey      5.10     David Shinskie     4.74
Cole DeVries       5.36     Tristan Crawford   5.15     Santos Arias       4.81
Dave Gassner       5.46     Matthew Fox        5.15     Jeremy Cummings    4.90
Jesse Floyd        5.57     Jose Mijares       5.17     Winston Marquez    4.93
                            Jason Miller       5.19     Alexander Smit     4.96
                            Brad Baker         5.35     Henry Reyes        5.16
                            Jose Lugo          5.39     Angel Garcia       5.40
                                                        Jesus Carnevales   5.70

Cole DeVries is an example of the various adjustments showing a pitcher in a worse light, because his nice-looking 3.41 ERA at low Single-A gets knocked down a peg with nearly every context adjustment. The Midwest League had a cumulative 3.78 ERA, which means that DeVries' 3.41 ERA there was the equivalent to a 4.03 ERA in a run-scoring environment equal to MLB. Beyond that, FIP shows that he pitched much worse than his ERA suggests.

DeVries had good control, but managed just 108 strikeouts in 148 innings and served up 17 homers in a league where power is rare, which is why his FIP was about 14 percent worse than league average. DeVries pitched worse than his ERA suggests and the pitcher-friendly environment that he played in means that his ERA wasn't as impressive as it looked to begin with, and he was also old for low Single-A as a 22-year-old who played three seasons at the University of Minnesota.

Consider that DeVries was in the same rotation as Tyler Robertson, whose FIP was 39 percent better than the MWL average as a 19-year-old with zero college experience. Robertson dominated a league filled with much older, more experienced players and his 2.48 adjusted FIP ranks second to only Kevin Slowey among pitchers with at least 100 innings. Meanwhile, DeVries goes from a raw ERA of 3.41 to an adjusted FIP of 5.36, which was fourth-worst among 18 pitchers who tossed at least 100 innings.

The best pitching season turned in by a Twins minor leaguer in 2007 came from Bradley Tippett, a 19-year-old Australian right-hander who went 7-1 with a 0.93 ERA and 51-to-4 strikeout-to-walk ratio in 38.2 innings out of the bullpen at rookie-level Elizabethton. Tippett's FIP nearly matched his incredible ERA, he served up just one homer to go along with the fantastic strikeout-to-walk ratio, and he was the same age as the rest of the league. It was nearly a perfect prospect season.

Elizabethton's bullpen also included Michael Tarsi, Michael McCardell, and Spencer Steedley, who posted numbers that were just slightly less dominant than Tippett. However, while Tippett was a teenager, Tarsi was a year older at 20 and both McCardell and Steedley were 22. Rookie-ball numbers should be taken with a grain of salt to begin with because of the small sample of games involved and rookie-ball numbers from 22-year-olds are far less impressive than they initially appear.

Along with Slowey's excellent 2.40 adjusted FIP, Scott Baker (2.75) and Matt Garza (2.86) were also great at Triple-A before combining to post a 4.20 ERA in 293 innings with the Twins. Nick Blackburn's 2.36 raw ERA in 148.2 innings between Double-A and Triple-A might suggest that he should also be included in that group, but his 3.74 adjusted FIP wasn't on the same level as Slowey, Baker, and Garza before he got lit up for 12 runs in 11.2 big-league innings.

Much has been made of the notion that the Twins' minor-league system boasts tons of high-quality pitching depth while being devoid of quality position players. My analysis of the 2007 numbers shows that to have been true this season, because the organization's No. 1 hitter had an adjusted OPS that was about 31 percent above average, while a total of 11 pitchers had an adjusted FIP that was at least that good.

The Twins' system contained 17 pitchers who were at least 20 percent better than average this season, while only four hitters could say the same. On the other hand, the number of players who were simply above average in 2007 was relatively close, with 35 pitchers and 30 hitters. Plus, if you look only at hitters with at least 250 plate appearances and pitchers with at least 250 batters faced, the picture is somewhat different:

                       FIP%                            OPS%
Kevin Slowey           1.47     Wilson Ramos           1.31
Robert Delaney         1.47     Deibinson Romero       1.23
Tyler Robertson        1.45     Jose Morales           1.20
Matt Garza             1.36     Trevor Plouffe         1.17
Eduardo Morlan         1.35     Luke Hughes            1.15
Anthony Swarzak        1.30     Brock Peterson         1.13
Yohan Pino             1.22     Joe Benson             1.13
Oswaldo Sosa           1.22     Brian Buscher          1.12
Ryan Mullins           1.22     Danny Valencia         1.11
Michael Allen          1.21     Matt Tolbert           1.11
Jeff Manship           1.19     Alexi Casilla          1.11
Jay Rainville          1.19     Chris Parmelee         1.10
Alex Burnett           1.18     Matthew Macri          1.10
Zachary Ward           1.18     Rene Tosoni            1.10
Nick Blackburn         1.17     Brian Dinkelman        1.09
Brian Bass             1.17     Ozzie Lewis            1.08
Joshua Hill            1.14     Brandon Roberts        1.07
Brian Duensing         1.14     David Winfree          1.07
Kyle Waldrop           1.12     Steven Tolleson        1.07
Armando Gabino         1.10     Juan Portes            1.05
Julio DePaula          1.08     Garrett Guzman         1.05
Jay Sawatski           1.08     Johnny Woodard         1.05
Bobby Korecky          1.07     Garrett Jones          1.05
                                Dustin Martin          1.04
                                Denard Span            1.04
                                Erik Lis               1.02
                                Tommy Watkins          1.02
                                Rashad Eldrige         1.02
                                Rene Leveret           1.02

The organization's top-level pitching is still far more impressive than the top-level hitting, but in terms of above-average performances from players who either batted 250 times or faced 250 batters, there were 23 pitchers and 29 hitters. There are indeed a ton of high-quality pitching prospects in the Twins' minor-league system and they lack the same type of high-quality hitters, but the position-player depth is better than advertised. Still, pitcher-friendly environments and all, the Twins' pitching depth is great.