The short version of what's coming: Pitchers do not fear Billy Butler anymore.
This past offseason, the Royals had a choice. They could exercise Butler's option for $12 million, or they could let him walk and fill the DH role through a committee or through a dedicated player. The team chose Kendrys Morales, another plodding type guy, and hasn't looked back.
It's all sad business, you know. For years, among terrible Royals teams, Butler was often a lone bright spot in the lineup. A professional hitter, some might say. The only guy who could take a walk and still do some damage when he made contact. Last year saw those skills decline, and the Royals decided it was time to move on from the homegrown sauce man known affectionately as Country Breakfast.
Butler's decline has continued in Oakland. Butler is currently slashing .253/.301/.354 (86 wRC+). Everything points toward Butler having lost what he once had. We saw the beginning of it last year. His power disappeared. His walk rate sunk to a career low. His plate discipline took a rare hike in the wrong direction (increased rate of swings at pitches outside the strike zone). His rate of first pitch strikes seen increased. Pitchers challenged Butler, and he responded by being more aggressive. Unfortunately, it's not paying off.
Butler is still making contact. He hasn't lost that ability just yet. However, nothing good is happening with that contact, and it's worse than last year. Butler is pounding the ball into the ground (highest grounder rate of his career), and he's not hitting line drives to make up for it (second-lowest line drive rate of his career). He's popping up more than ever. In addition, the balls he is elevating are doing diddly-squat--his batting average and slugging percentage on fly balls has never been lower. If my calculations are right, out of the 58 fly balls that Butler has hit this season, only 3 have been pulled.
Pitchers are throwing Butler more strikes, and Butler can't do much with those strikes. If pitchers are throwing more strikes, he certainly isn't going to walk more. Butler could be at the point in his career where he needs to start pulling the ball a ton in order to have some semblance of production. That's basically what Nelson Cruz is doing, though it's a bit more complicated than that in truth.
The Royals made the right choice; there was no reason to give Butler a multi-year contract. Instead, the team chose Kendrys Morales, who is currently slashing .292/.358/.478 (132 wRC+). Morales' walk and strikeout rates are not out of line with career norms; in fact, each is slightly better. Pitchers last year challenged Morales like they did Butler; his rate of first pitch strikes seen was up. Pitchers perhaps increased their rate of pitches within the zone, taking advantage of Morales' tendency to chase. Fangraphs' two sources of data disagree in this regard, so it's possible that pitchers just moved pitches that were far out of the zone to the border of the zone.
This year, pitchers have decreased their rate of first-pitch strikes, but they may be increasing their overall rate of pitches within the zone to Morales, who has increased his rate of swings within the zone. Again, Fangraphs' two sources disagree on whether Morales has seen more pitches in the zone this year. Again, I'm guessing that pitchers have moved borderline pitches closer to the zone. Morales is punishing pitchers this year for their transgressions.
Most importantly, Morales is elevating the ball in the way that Butler isn't. After four years of a high ground ball rate for a plodding guy, Morales has a grounder rate more similar to 2009 than 2010-2014. Morales is putting the ball in the air more, which helps him avoid the damage done by the shift (Morales pulls most of his ground balls from both sides of the plate). Though Morales is not pulling the ball more in the air, he's making much more solid contact than Butler. His popup rate and home run per fly ball rate have both rebounded from his shortened season last year. His batting average and slugging percentage on fly balls and line drives have also rebounded. Morales is definitely doing damage in the air.
Now, when considering the rest of the season, an average of Steamer and ZiPS rest-of-season projections puts Butler and Morales at about equal production (109.5 wRC+ vs. 111 wRC+). However, I think the evidence is there that Butler can't make solid contact anymore, whereas Morales has rebounded after his miserable 2014. The Royals' choice is working out well now, and it should continue to work out well for the rest of this season.