I Want Boof Bonser (Cubs Edition)

As a Cubs fan, the fragile nature of the team's 2010 rotation (especially given the slew of injuries that plagued the team in 2009), worries me. With the departure of Harden and with Lilly's injury, I am concerned about what to expect from what used to be one of the NL's top rotations. I do not want to see Jeff Samardzija or Carlos Silva spot starting or, god forbid, being handed a rotation slot. Gorzelanny showed significant improvements in his strikeout and walk rates in both the majors and minors last season, so there is reason for optimism with him in the #5 spot of the rotation. However, there is no legitimate reason for the Cubs to gamble on him as being anything but a serviceable fifth starter; at least not if they want a legitimate shot at winning the NL central in 2010. This means Marshall will probably have to spend sometime in the rotation, leaving an already thin bullpen even thinner.

Given the overall lack of quality pitching depth on the team at the moment, I propose the following and most likely controversial solution: acquiring Boof Bonser from the Red Sox. Bonser, who has a career 5.12 ERA and 1.45 WHIP in 391.2 IP, is out of options and unlikely to break camp with the Red Sox. Thus, he would have to clear waivers to be optioned down the minors. The likelihood that he will be either traded or essentially given away in a waiver claim, therefore, is high. The Cubs should pounce on the opportunity, should it arrive. Here's why.

Despite the horrendous results, Boof Bonser has not been a horrendous pitcher. While playing in the AL (granted, the AL Central), Bonser has accumulated a career 7.28 K/9 and a strong 2.87 BB/9 with a 40+% GB rate to boot -- sure signs of potential. The reason for the poor ERA and WHIP seem to be poor luck. His career BABIP is .326 (league average was .304 last season); his LOB% in 2007 and 2008 were 69.6% and 57.9%, despite the league average being 70.7% and 71.4%, respectively. Furthermore, Bonser has a career HR/9 rate of 1.40, despite a career GB rate of 42.9% (resulting in an unlucky 12.3% career HR/FB rate). Despite all of his struggles in the major leagues, Bonser's career xFIP is a promising and significantly less ugly 4.30 mark. A 4.30 xFIP isn't exactly going to light the world on fire, but it shows that he has not been the complete disaster his ERA says he's been. It is worth noting that Bonser's sample size is very limited and many people forget that he has the pedigree for success (first round pick in 2000; he was the intended centerpiece of the A.J. Pierzynski deal between the Giants and Twins in 2003).

In figuring out what Bonser could provide the Cubs, I am going to utilize his career 4.30 xFIP and 7.28 K/9 as the baseline for this analysis, which is actually a bit pessimistic, in my opinion. Given that he is recovering from rotator cuff and labrum surgeries which forced him to miss the 2009 season, let's limit his innings threshold to 100.

In moving from the AL to the NL, The Hardball Times found that, on average, a pitcher's K/9 rate would rise by 0.57 per nine and that their ERA would fall by 0.41 runs. Accounting for these factors, Bonser would have a prospective 3.89 ERA and 7.85 K/9. Over 100 IP, that would be 43.22 runs allowed.

Next, we account for a change in park. Through the 2008 season (Bonser's last year of play), the Metrodome suppressed run scoring by 4%, whereas at Wrigley through last season, the park exaggerated run scoring by 8%. This 12% swing would inflate Bonser's runs allowed to 48.63.

Finally, we need to accord for defense. Last season, the Cubs allowed 19.8 runs to score compared to the league average defensive posture. Stated otherwise, the Cubs had allowed -19.8 Fielding Runs Above Replacement (FRAR). However, out goes Milton Bradley (-4.1 FRAR), Jake Fox (-6.7 FRAR), Aaron Miles (-2.7 FRAR), Joey Gathright (-0.9 FRAR), and Reed Johnson (-1.2 FRAR) and in comes Marlon Byrd (-1.0 FRAR), while Alfonso Soriano (-10.8 FRAR last season) has a 3-year UZR/150 in the OF of +5.8 (let's just say his FRAR in 2010 is completely neutral, though CHONE pegs it to be positive). In theory, that is a +25.4 FRAR swing in the right direction; a rough +5.8 team FRAR projection for 2010. Last season, the average team played 1442 innings of defense, so the Cubs would be preventing a mere +.004 runs per inning played compared to the league average defense. Over 100 innings, this would essentially save Boof Bonser just under one-half of a run, bringing his projected 2010 runs allowed total on the Chicago Cubs to 48.22.

In my estimation, therefore, over 100 IP, Bonser would post an ERA of 4.34 with 87 or so strikeouts. Given an expected (and sharp) regression in BABIP, I would expect the WHIP to tumble to the 1.35 or so range. Bill James says 1.38.

Could be worse, right?

But that's not necessarily the reason why I want the Cubs to acquire Bonser. Despite the lack of starting pitching depth, it's the lack of bullpen depth that scares me more. According to Tom Tango his publication The Book, the difference between a pitcher's ERA as a starter versus a reliever is about one run. If true, this would make Boof Bonser a sub-4 ERA relief pitcher who strikes out his share of guys, keeps the ball on the ground at a respectable rate, and does not walk too many batters. Given the state of the Cubs bullpen -- many high walk, flyball pitchers -- Bonser could prove to be a valuable asset for the team at a low price. Given the loss of Guzman and the price tag of Jason Frasor, I say the Cubs consider it.