Through the first half of last season, the Royals as a team batted .274 / .324 / .408 for a 99 wRC+, almost exactly league average. They were very similar in the second half of 2015 as well - a 100 wRC+ on a roughly equivalent batting line, give or take a few points here and there.
This year through the first half of the season, the Royals hit .272 / .320 / .412. That’s pretty similar to last year, give or take a few points here and there. However, instead of hovering around league average, that’s good for a 93 wRC+. The Royals have gotten worse without actually getting any worse.
This year’s change in run environment has been mentioned at this website in the context of the Royals pitchers. Not surprisingly, a league-wide increase in home run rate does not treat fly-ball prone pitchers very well despite the home park. The biggest problem has been away, naturally, with a 1.6 HR/9 on the road this season. A 1.1 HR/9 at home is better, but the Royals gave up only about 1.0 HR/9 in total last year.
Something similar applies to the hitters. The Royals do not specialize in hitting dingers, though there is some power increase for individual players. With 14 home runs, Salvador Perez is seeing a big increase in power at the expense of contact (almost entirely out-of-the-zone contact; his within-zone contact rate is about the same). Eric Hosmer seems poised for his first 20+ HR season in the majors and is currently running a career-high ISO. Kendrys Morales has been smashing the ball lately.
Despite those increases, the Royals are 27th in MLB in home runs with 81. It’s not like the Royals have been unlucky, either - their .320 BABIP in the first half ranks 6th in MLB. Unfortunately, what this has all led to is 352 runs, good for 25th in MLB.
The contact-oriented spray approach, which has worked in the past, appears to be falling short this year. The Royals hitters are seeing a similar home/road split - they’re above average at home, and they stink on the road despite similar batted ball profiles. They are hitting the ball a little less hard and popping up a bit more on the road, but those alone should not be responsible for the large gap. A 107 wRC+ at home and 81 wRC+ on the road is a huge gap.
The Royals and fans have talked about the team just feeding off the energy in Kauffman Stadium, and somehow that has elevated their play. However, every team every year plays half their games on the road, including the Royals last year. Their 106 wRC+ at home last year is about the same as this year. Their 93 wRC+ on the road last year is much better than this year’s. I’m not sure the energy of Kauffman can be blamed.
Can their batted ball approach be blamed? Maybe in part. Most of the rest of the league has found something. Something that has returned home run rates to their highest since FanGraphs started tracking the stat (HR/FB).
I’m not necessarily saying the Royals should change what they’re doing. Ride the horse that got you there and all that. This current level of offense may not even last for the rest of the season. Maybe the Royals get better when injuries have taken less of a toll. Who knows. They still have to play better on the road. Whether the Royals can find something else, something of their own making and identity to bring up their offense on the road, remains to be seen.