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The Misconceptions of Aaron Cook

In just a matter of three hours today, two reporters close to the team expressed concern over the Rockies' "ace" getting back on track; Harding in his notes column, and Renck on XM Radio's Baseball Beat.  Such concerns haven't escaped these boards either, as more than a few have expressed some mild concerns over Aaron Cook's recent outings at home.

If you don't want to read a drawn out or boring (to some) explanation, I'll cut to the conclusion right here:  Relax, this is the same Aaron Cook of 2006, and with a few very slight corrections in his command and some bigger ones in luck, he'll be pitching more to expectations in short time.  If you care to know why, just keep reading...

For starters, Aaron Cook doesn't have the numbers to carry the "ace" label very well, but that doesn't mean he isn't without value.  Cook doesn't have the K's you'd expect of a real "ace" in the Beckett mold, but he does a pretty good job of limiting walks and keeping the ball on the ground.  Because Cook only strikes out 3.01 batters per nine, he allows quite a few balls in play.  When he struggles, it's most often because all those grounders aren't finding gloves, and when sprinkled with the occasional line drive, or even the rare homer, he'll give up a couple runs.  Yet, because his GB% is so high, when Cook is off, he's merely frustrating, and not necessarily bad.

So what's the difference this year?  Nothing really.  His GB% is a staggering 57.1%, down only .7% from last year.  The K rate is down and the walk rate is up, but neither is beyond a mild fluctuation that comes with a new sample.  Basically, to get these rates back in line with last year, it would take an extra K and one less BB ever game or two.  These have caused his K/BB rate tighten, but it was never good in the first place, so why worry about it now?  It isn't extra homers, as both the HR/FB% and HR/9 are an eyelash better than last year.  Luck through BABIP?  Nope, it has gotten better, but within reason.  To date, Aaron Cook's numbers are hardly different from last year's numbers.  Even if you quibble with the K's and BB's, it would take very modest improvements to bring them back to last year's levels.

What is he doing different at home than?  HE may not be the problem.  Fan Graphs provide excellent visuals to break this down.  If you look at the graphs for K/9, BB/9 and HR/9, you'll see that he's either repeating a trend, declining but within reason, or improving.  He's not pitching that much different at home than he has in the past.  So where's the problem?  The biggest issue with his home numbers may come from the pitchers that follow him.  When Cook leaves runners on while on the road, the relievers behind him have slammed the door on runners over 80% of the time.  At home, they've been much more generous, stranding only about 55%, a difference close to 30% in strand rate depending on the park.  I don't know how many runs this has amounted to, but when you look at Cook's expected ERA, or FIP at around 4.62, these runners allowed to score at home could be the reason Cook's ERA is higher beyond the general inflation felt by pitchers while at Coors.  

In summation, Cook's last outing wasn't great, but was an outlier to his season.  There isn't much he needs to do to regain his form at home.  If the Rockies want to see Cook's numbers pick up at Coors, perhaps they should re-examine who they have following his exits.  Improve the relief immediately following Cook, and the numbers will follow.