At 29, Edwin Jackson has already played for seven major league teams during his 10-year career. After ranking highly in Baseball America's Top-100 prospect lists for a couple of seasons (No. 4 in 2003 and No. 30 in 2004), Jackson had a couple of middling seasons with the Dodgers before playing for the Rays, Tigers, Diamondbacks, White Sox, Cardinals, and Nationals. Theo and Jed signed Jackson to his first significant long-term contract -- a four-year, $52 million agreement -- this past January.
Over the past few years, Jackson has consistently posted average (18.5 K%) to above-average (20.0 K%) strikeout rates. Furthermore, Jackson's swinging-strike rate has also been above average (8.5 SwStr%) over the past several seasons.1 In fact, Jackson posted career-highs in K% (21.3 K%) and SwStr% (12.2 SwStr%) last year with the Nationals.
While it's difficult to identify the cause behind last year's spike in K% and SwStr%, the most notable change in Jackson's repertoire is his reduced dependency on his slider. According to PITCHf/x, Jackson's slider usage fell from nearly 43% in 2011 to 29% in 2012. The effectiveness of Jackson's slider rose in conjunction with the decline in usage: Jackson's wSL/C rose from .63 in 2011 to 1.02 in 2012. According to Baseball Info Solutions, Jackson's slider was the 18th most effective in baseball. His slider usage and effectiveness seem to be a key determinant of his strikeout successes.
Jackson has simultaneously cut down his walk rate to a much more respectable level. After posting walk rates close to and north of north of 10% for a few years, Jackson has been between average (8.5 BB%) and above-average (7.0 BB%) over the past four years.2
Jackson's BABIP is likely due for some regression to the mean over the next couple of years. He sported a .278 BABIP in 2012, which is well below his career .306 BABIP. Fortunately, Jackson's HR/FB should also regress after the extreme 11.7 HR/FB% that he posted in 2012. However, Jackson has had an issue with the long ball as his HR/FB% has been between average (9.5 HR/FB%) and well below-average (11.5 HR/FB%) over the past several seasons.3 Whenever we discuss home run rates, Wrigley's size becomes a concern. Last year, Nationals Park (1.044 HR park factor) was more homer-friendly than Wrigley (.962 HR park factor). We can also look at a hit chart that takes balls hit against Jackson in Nationals Park and overlays them onto Wrigley Field.
All things being equal, there are a number of doubles, triples, and fly outs that would have likely left Wrigley. While this is a concern, there are a number of other factors that may mitigate these issues: wind patterns and temperature being the two primary ones. The winds and temperatures of April and May should help Jackson keep the ball in the yard, while those of June, July, and August will be a little less helpful. Taking the park factors, hit charts, and external factors into consideration, the likely net result is that Jackson surrenders about the same number of home runs at Wrigley Field that he did in Nationals Park without taking regression to the mean into consideration.
Finally, there are a couple more noteworthy points to discuss regarding Jackson's durability and velocity. Since becoming a full-time starter in 2007, Jackson has started between 31 and 33 games each season, which is good for ninth-most during that time span, putting him ahead of pitchers such as Cole Hamels, Jered Weaver, and Roy Halladay.4 However, the high usage could have taken a toll on Jackson's arm, which is what indeed may have happened. According to PITCHf/x, his fastball velocity fell to 93.4 miles per hour last year, which is well below the 95.0 miles per hour he was throwing in 2007 and even the 94.5 miles per hour he averaged between 2008 and 2011.
While the Cubs have made a pretty large commitment to Jackson, the price that they will end up paying could wind up a bargain. Since the contract will cover Jackson's age 29 through 32 seasons, we should expect some skill degradation. The surplus value of the contract is dependent on how exactly we think Jackson will age. ZiPS has projected a 3.3 WAR season for Jackson in 2012. If we use this as our baseline and dock a half a win per year -- a conservative estimate, but one that may be justified by Jackson's past workload and recent velocity decrease -- the Cubs will come out about even on the contract.
While Jackson may no longer be of the quality to be a member of a championship-caliber pitching staff by the time 2015 and 2016 roll around, he will give the Cubs quality innings and contribute to a team that may have an outside chance of making the playoffs over the next couple of years. You'll see him in his first regular-season start for the Cubs Wednesday night in Pittsburgh.