The signing of Aaron Cook was largely seen as a move that would not effect the major league roster, but if next year has injury troubles anything close to what happened last year it’s a lock he does. His contract is worth $1.5 million if he is on the major league roster, but I am not sure if he has an out clause with deadlines that kick in if he doesn’t get added to the 25 man roster.
Cook is the prototypical groundball pitcher and that is pretty much his only skill. He has a career K/9 of 3.83 and a BB/9 of 2.80. Those might be some of the worst numbers around, but Cook has survived the confines of Coors Field for 10 seasons by doing one thing very well. His career groundball rate stands at 57 percent, which ranks 8th for pitchers from 2002-2011. That is behind pitchers like Brandon Webb, Derek Lowe and Tim Hudson. He does not compare to any of them in regards to strikeouts and is more like Fausto Carmona who finished one spot in front of him on that list.
He’s never been elite, but while pitching in Coors Field he has totalled an ERA of 4.53 and an xFIP of 4.40. Coors field inflates home runs by about 15 percent and wOBA by about 10 percent. Fenway on the other hand decreases left handed home runs by 21 percent (Cook struggles primarily against lefties xFIP 4.82 against LHH vs 3.97 against RHH). Even doubles won’t get much worse in Fenway Park.
One question that could make all the difference is defense behind a groundball pitcher. The metrics on the Rockies are mixed at best. From 2002-2011 the team held the fourth worst UZR in all of baseball at -170.6, but Total Zone puts them eighth with +76.9. That is a huge discrepancy over a large sample of 10 seasons. I tend to believe the UZR score based on the pitching staff accumulating the second highest BABIP in baseball during that span of .302, but it’s unclear how good or bad they really were.
When we talk about groundball pitchers though we need to focus on infield defense. Cook had a large portion of his time with Todd Helton manning first base and his defense was some of the best. There has been a constant change at Second and Short over the years and both grade fairly neutral. On the other hand third base has been a hole and cost Rockies pitchers 42.8 runs over 10 seasons with a UZR/150 of -3.8. This is one of the places though that Total Zone disagrees and makes it a tough call.
The Red Sox did have some struggles on the right side of the infield in 2011, but much of that was Jed Lowrie and Mike Aviles who will not be manning those spots in 2012. Kevin Youkilis struggled in full time duty at third base, but health is the question and likely dragged down his defense last year. The other side includes two of the best in Dustin Pedroia and Adrian Gonzalez. This defense helped the team maintain a solid BABIP of .285, which is right near league average. Cook has only seen a BABIP of .285 once in his career and perhaps that is partly a poor skill effect, but defense does have a large effect on it.
How many innings he can throw is a huge question and Cook has had plenty of shoulder troubles. This probably had something to do with his walk rate going up in 2010 and 2011 leading to huge troubles in his short seasons with ERA’s over five both years. His FIP in both seasons were not quite as scary though, at 4.54. That isn’t going to save the rotation, but fills a potential spot with league average production and at a very cheap $1.5 million dollars. Once you account for defense, league and park changes I would expect a healthy Cook to be at career levels with an ERA around 4.4.
The Red Sox still have to look to add Hiroki Kuroda or Roy Oswalt to really solidify the rotation, but in my opinion a healthy Aaron Cook is enough to make the team take a pass on Joe Saunders who has been league average by beating his FIP. He will likely cost about $4 million dollars more and has similar risks as his ERA has been over 4.4 in all but one season while in the AL. This all makes Cook a good medium return, but high risk attempt by the Red Sox.