In 2012, after 10 starts, the rotation averaged just over 5 innings per start. In 2013, after 10 starts, the rotation averaged just under 6 innings per start. Improvement!
In 2012, the rotation had a 6.49 K/9 and 4.38 BB/9, which was awful. In 2013, the rotation had an 8.65 K/9 and 1.97 BB/9, which puts the Royals 4th in MLB in both categories, which is absolutely fantastic. Improvement!
I would like to note here that I do prefer K% and BB% instead of K/9 and BB/9 since starters rarely pitch 9 innings, but since I used K/9 and BB/9 last year, I wanted to stay consistent for comparison's sake.
In 2012, the rotation had a 1.52 WHIP. In 2013, the rotation had a 1.30 WHIP. Improvement! The Royals rank 15th in the MLB in WHIP, but there is very little separating the middle third of MLB in WHIP.
So, by those measures, the rotation has vastly improved from last year. They pitch longer into games, and they strike more guys out while walking fewer. Unfortunately, the Royals have been a bit unlucky so far since the staff has a .320 BABIP, which ranks 25th. To compensate for that unluckiness, the Royals have a 77.2% strand rate, which ranks 8th. While guys are getting hits, the Royals are not allowing many of those runners to score. Having a high strikeout rate and low walk rate helps prevent those runners from scoring.
The burning question here, though, is this: Is this performance sustainable? It's possible. I expect the K% rate and BB% rate to regress to the mean, but I think this staff is capable of above-average rates in both categories. Just not as great as they are now. Guthrie and Mendoza have never shown high K% rates, but Santana and Shields have in the past. Davis is the unknown. Partially compensating for the regression in K% and BB% will be an improvement in BABIP. I don't think they'll allow a .320 BABIP all year. Another factor is the LOB% (the strand rate). I think that will regress a little bit, too, due to a lower K% and a higher BB%. When Danny Duffy and Felipe Paulino return will be a progress check point. If it is difficult to find starting pitching spots for those two guys, the Royals will be in a good situation. If those two easily replace two of the current starters, then the Royals will probably not be in the hunt for the playoffs.
Overall, the starting rotation as a unit has been in the top 5 in MLB in the first 10 games. I don't think that is sustainable. A top 10 rotation is possible, but I think a top 15 rotation is the most likely. After a 2012 rotation that ranked near the bottom 5, I'll take the improvement.