The Impact of Switching Leagues For Pitchers

August 2 3:45am
Derek Carty

Edwin Jackson tradeThis past weekend was the MLB Trading Deadline, and boy was it a busy one. Players were changing hands left and right with a total of 18 semi-major deals going down before all was said and done.

While a change of team and environment can have a significant impact on a player’s value, his FanDuel price doesn’t take this into account. FanDuel price is largely calculated using the player’s past performance in his old environment. As such, there is value to be had for players changing teams at the deadline. Last week, I began looking at one of the most important variables that we need to consider when assessing a player’s new value: league change.

When a player is traded from the National League to the American League (or visa-versa), he is, of course, going to be surrounded by new teammates, new coaches, and new philosophies—essentially, an entirely new environment—but perhaps more important than all of that, he’ll be facing a new level of competition. While you might not initially think that there’s a big difference between the AL and the NL—after all, everyone is in the major leagues, at the highest level of professional baseball in the world—there are some important differences that we can take note of.

Last week, I examined how hitters perform when they cross over leagues. Today, I’m going to do the same for pitchers.

The Process

To study the effects of changing leagues, I’ve looked at all pitchers who played in both the American League and the National League in the same year. Weighting by the shorter of the two stints, I looked at average change in performance for all players between 2000 and 2010. I did not adjust for park, which would likely make a small difference, but the relatively large sample should drown out some of those effects, and this should still provide us with a pretty good gauge. These results are to be read as if an AL pitcher is moving to the NL, and you would simply take the inverse if you’re looking at an NL pitcher moving to the AL.

The Results

Like we saw last week, there is a very clear trend of pitchers performing better in the National League than the American League, all else equal, and the effects here are much, much larger than for batters. Pitchers tend to strike out lot more batters, adding an entire half-point to their K/9 rates. Their BB/9 is essentially unaffected, experiencing the tiniest decrease. They do add a point and a half to their groundball rate, though, rounding out their “big three” skill indicators.

In terms of home runs allowed, it’s interesting to note that their HR/FB ratio—that is, the percentage of their outfield fly balls allowed that turn into home runs—increases, but they allow fewer home runs overall; the increase in groundball rate and subsequent decrease in fly ball rate makes up for the difference. That is, while fly balls become homers more frequently, pitchers allow them less frequently for a net decrease in total homers. The BABIP effect is also quite large, with pitchers cutting 0.009 points off of it with the move to the senior circuit.

There are also smaller effects, like pitchers winning one percent more of their games and pitching one-third of one-third of an inning more, but these things are largely negligible.

Add all of this up, however, and pitchers will shave nearly a half-point off their ERA if they’re fortunate enough to be traded to the National League. That’s enormous!


While the effects we witnessed for hitters last week were relatively small, the effects for pitchers are absolutely enormous in comparison. Pitchers will improve almost across the board with a trade from the AL to the NL; especially important for FanDuel owners are the improvements in strikeouts and earned runs.

Following this year’s trade deadline, starter Ubaldo Jimenez and notable relievers Mike Adams and Trever Miller figure to be subjected to a league-related decline in value as a result of their move to the AL. In comparison, starters Edwin Jackson and Alex White and notable relievers Octavio Dotel, Marc Rzepczynski, and Brad Ziegler figure to gain a boost from their moves to the NL.

Of course, like I mentioned last week, we need to remember to take things like parks, defense, offensive support, etc into account. So while Ubaldo loses value moving to the tougher league, he will gain value in terms of ballpark but will lose some more due to less offensive support. Overall, Ubaldo will see a net loss, which is important to consider when selecting your FanDuel pitcher. On the other side of the spectrum, though, is Edwin Jackson, who gains value in nearly every conceivable way: better league, better park, better offense.

Concluding Thoughts

That wraps it up for this week. Next week, I’ll be checking out how pitchers fare when they change leagues. As always, if you have any questions, feel free to comment or e-mail me. Also, be sure to add me as a friend on Facebook and follow me on Twitter.

Derek Carty’s work can also be found at Baseball Prospectus, CardRunners Fantasy Baseball, and He has previously had his work published by The Hardball Times, NBC’s Rotoworld, Sports Illustrated, FOX Sports, and USA Today. He is the youngest champion in the history of LABR, the longest-running experts league in existence, and is a graduate of the MLB Scouting Bureau’s Scout Development Program (aka Scout School). He welcomes questions via e-mail, Facebook, or Twitter.

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