The return of Sweet Chen Music

Ned Yost decided to shake up the Kansas City Royals pitching rotation for the first time this season a few days ago, removing Luis Menodza as a starter and replacing him with Bruce Chen.

First of all, it's fairly amazing that this is the first change to happen to the rotation in 2013. Will Smith started one game during a double-header, but the rest of the 88 starts have gone to the same five pitchers. You can certainly argue that Mendoza or Wade Davis should have been removed already, but it's also impressive that no one has missed time with an injury.

Mendoza's last two starts were unmitigated disasters; a combined 5 2/3 innings, nine runs, 11 hits, six walks, three strikeouts. Overall, Mendoza had been slightly worse this season than he was last season, but still owns a 4.50 FIP, not-awful for a No. 5 starter.

Yost indicated to Spencer Fordin of MLB.com that Mendoza's workload over the winter gave the right-hander an advantage over the southpaw in Spring Training, but is also factoring into the team's decision to swap the two pitcher, telling the reporter that the swap was planned:

"That was kind of the plan all along. [Mendoza] had pitched winter ball and was in a spot where he could be highly competitive in Spring Training. Bruce is always a slow starter in Spring Training, so we made a decision early knowing that, at the halfway point, if Mendy was struggling a little bit, we'd have a fresh Bruce, a Bruce that's won more games than any pitcher we've had over the last three years. Hopefully, Bruce will step in and finish it out strong."

Sometimes, I think Brian Kenny's "Kill The Win" campaign is overstated, but that Yost quote is making me reconsider my stance.

Anyways, if you believe Yost, everything is going according to the process. But should the team be replacing Mendoza with Chen in the rotation?

Chen had his worst season as a Royal last season, posting a 5.07 ERA over 34 starts. The lefty's 4.73 FIP suggests that he may have been a bit unlucky, but he still had little business as a starter.

This year, Chen is 3-0 with a 2.41 ERA in 19 appearances out of the bullpen. Judging by those statistics, the veteran has earned his spot in the rotation. More advanced statistics, however, suggest that Chen is essentially the same pitcher this year that he was last year.

The table below lists some of Chen's statistics from the past two seasons:

Pitchers are normally more effective out of the bullpen than as a starter, so it's a bit discomforting to see Chen striking out less people and walking more as a reliever. Chen has only thrown 33 2/3 innings this season, but we have no reason to believe he has made any improvements.

The southpaw has a shiny ERA because he has stranded more runners than he usually does, and allowed fewer home runs. We can expect both of these numbers to regress towards his career average numbers, which will lead to more runs by Royals' opponents.

ZiPS projects Chen will post a 5.00 ERA and 4.72 FIP the rest of the season, making eight starts in the process. Steamer is a bit more kind, projecting 4.45 ERA and 4.61 FIP over 11 starts. Neither projection system, however, sees Chen as an improvement over Mendoza during the second half of the year.

Maybe Kansas City will catch lightning in a bottle, and Chen can out-pitch his peripherals for a little while. I certainly don't expect that to happen, but it is a possibility.

Chen is more likely to struggle tonight against the Cleveland Indians at Progressive Field, and continue to struggle until Yost removes him from the rotation. The Royals may have planned for this switch to happen, but there is little reason to expect their plan to work.