Comparing last season's rental pitchers

I thought I had it all figured out. It had happened to my beloved Blue Jays when Josh Johnson moved from the Miami Marlins to Toronto and promptly became terrible. Pitchers who move from the National League to the American League need an adjustment period; the designated hitter is a lot to deal with. Case closed.

But, like so many other times, I was proven wrong. The answer is never simple.

As #LesterWatch wound down into the wee hours of the morning last night, I started to think, is the team who actually signs him fully aware of what they will get? Was Oakland? Do you think Beane would do it again? Let's take a look at the pitchers who moved this past trade deadline.

xFIP
Pitcher	Pre-trade	Post-trade	Career
Justin Masterson	4.03	4.22	3.85
David Price	2.70	2.89	3.37
Jeff Samardzija	3.19	2.96	3.63
John Lackey	3.32	3.85	3.98
Joe Kelly	3.70	4.46	4.14
Jason Hammel	3.21	4.15	4.12
Jon Lester	3.00	3.27	3.67

HR/FB
Pitcher	Pre-trade	Post-trade	Career
Justin Masterson	10.2%	26.1%	10.5%
David Price	11.2%	6.2%	9.2%
Jeff Samardzija	8.5%	12.3%	11.0%
John Lackey	11.5%	12.2%	9.6%
Joe Kelly	12.0%	11.1%	10.3%
Jason Hammel	9.3%	15.3%	11.0%
Jon Lester	6.5%	8.5%	9.4%

David Price, John Lackey and Joe Kelly will all (presumably) start 2015 with the same team so we'll leave them out of this. That leaves Jeff Samardzija, Jon Lester, Jason Hammel and, most curious of all, Justin Masterson the focus of this 'buyer beware' article.

Jeff Samardzija and Jason Hammel are the most like Josh Johnson in that they moved from the National League to the American League. Samardzija really proved my aforementioned hypothesis wrong, not that it was ever right. In 17 starts with the Chicago Cubs, Shark pitched 108 innings of 3.19 xFIP baseball. But, upon moving to O.co, Samardzija improved to a 2.96 xFIP over 111.2 innings in 16 starts.

Of course, Fielder-Independent Pitching isn't for everyone, so Samardzija's only struggles -- and there weren't many -- in the American League were largely due to fewer ground balls (52.5% with the Cubs down to 47.9% with the Athletics) and more home runs per fly ball (8.5% with the Cubs, 12.3% with the A's). If I were a general manager, I'd look at that HR/FB rate as the outlier. O.co Coliseum is one of the better pitcher's parks in baseball, regardless of the designated hitter residing there. Over the past five seasons, its Batting Park Factor is 91.8 according to my own model and went over 100 in only one of those seasons (2010). I'm confident Chicago's American League affiliate got the pitcher they wanted.

The Chicago Cubs signed Hammel back after trading him away to the Oakland Athletics this past season. When he got traded he wasn't the star attraction of the deal, but over 108.2 innings he earned a respectable 2.0 fWAR for the Cubs. Upon moving to the A's Hammel had some terrible outings, watching his xFIP bloat from 3.21 to 4.15. His HR/FB and GB% shared the same fate as Samardzija but to a greater extent moving from 9.3% to 15.3% and 41.5% to 37.1%, respectively.

If I were Hammel, I too would have retreated back to the National League to raise my stock once again. He is comfortable there and has never had a negative WAR season while pitching for a National League team. The Cubs almost definitely know what they're getting: steady performance and a potential mid-season trade chip. The question still remains: why can't we better predict a pitcher failings like Hammel's when switching leagues or teams midseason?

Justin Masterson was the one that really blew my mind. My hypothesis only suggests pitchers will do poorly when switching from the National League to the American League. What this implies then is that when the opposite happens, a pitcher from the American League will flourish in the National League. Obviously Masterson is just one example and a very small sample size, but it's extremely interesting nonetheless. Masterson earned 0.8 fWAR as a Clevelander with a 4.03 xFIP. By no means outstanding. After being traded to the St. Louis Cardinals, Masterson's xFIP grew to 4.22 while his FIP grew from 4.08 to 5.84. This disparity is largely because of Masterson's inflated HR/FB rate moving from 10.2% -- around career-average -- to an unbelievably unsustainable 26.1%. More than a quarter of fly balls hit off Masterson in his short 30.2 innings of work as a Cardinal left the park.

But wait, it gets better. The last time Masterson switched teams mid-season was back in 2009 when he got traded from the Red Sox to Cleveland. As a member of the Red Sox that season, Masterson had a very good 3.71 xFIP. Can you guess what happened next? Masterson's xFIP inflated to 4.36 after the trade. However, in his first full season in Cleveland, Masterson settled into a 3.87 xFIP. I wouldn't expect those numbers from him again, but I think more stock can be put into those numbers than can be put into Masterson's short tenure at Busch Stadium.

That leaves only Lester, and he didn't switch leagues last season.

But he will starting next season. Unlike Masterson, he will get the benefit of having the whole season routine. I think that makes this way more of a sure bet for Chicago than a mid-season acquisition. For Lester, last year's move was the same story as the last three: inflated xFIP with a growth in HR/FB rate. This should probably prevent me from ever being scared of a pitcher moving from NL to AL ever again.

The Chicago Cubs still have a long way to go, but if only for pity of the franchise, I hope this does mark a turning point. Whether we're closer to understanding what a pitcher is worth in a midseason transaction is still debatable, but I think the savvy front offices will be very cautious moving forward. It's difficult to think of any of the aforementioned trades as 'worth it.' Pitchers made available at the trade deadline are a dangerous-looking commodity, and I don't think a lot of general managers envy Billy Beane's position right now.

. . .

All statistics courtesy of FanGraphs.

Michael Bradburn is a Contributor for Beyond the Box Score. You can follow him on Twitter at @mwbii. You can also reach him at michaelwbii@gmail.com