"It's just always trying to work on what feels the best, what's most comfortable," Kluber explained. "Early on in the year, guys were jumping all over the two-seam early, so it was kind of a little bit of an adjustment to that. Then, we got to the point where we felt pretty comfortable throwing both of them. It's not a concerted effort to throw one or the other. It's just having the ability to throw both of them kind of adds to your arsenal."
After throwing the four-seamer only 3.9 percent of the time during the 2014 campaign, Kluber has fired the pitch 21.1 percent of the time this year. As a result, his two-seam percentage has dropped to 30.4 percent this season, compared to 48.6 percent a year ago.
The biggest change has come when Kluber is ahead in the count or has two strikes on a batter. In those situations -- both to lefty and righty hitters -- he has relatively even percentages of four-seamers and two-seamers. The two-seamer remains the primary fastball for Kluber for the first pitch, or when he is behind in the count or in an even-count scenario.
"At times throughout the season this year," Indians pitching coach Mickey Callaway said, "maybe he was getting a little more flat run on his two-seamer than he wanted. So, he started using it a little bit more. Last year, obviously, he was in such a good place with throwing everything that he kind of stuck with one approach and didn't have to adjust.
"I think this year, he probably hadn't been in that same unbelievable zone, which you can't expect, so he's having to adjust. It's, 'OK, I'm going to throw a four-seamer here to get the effect I want, instead of my two-seamer running back to the middle.' So, I think that's probably what you're seeing.
"And, that used to be his main fastball. So, I think with all the success he's had and things like that, he probably feels comfortable with, 'Hey, now I can add another part of my game again, and continue to improve.'"
Jordan Bastian is a reporter for MLB.com. Read his blog, Major League Bastian, follow him on Twitter @MLBastian and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.