Herrera, 23, had a phenomenal season in 2012 pitching out of the Royals' bullpen. Appearing in 76 games during his rookie season, Herrera posted a 2.35 ERA with a 1.186 WHIP and 8.2 K/9.
This year, Herrera saw his K/9 just to 10.6, but seemed to lose his control as his walk rate rose and, more importantly, he began allowing large numbers of home runs. In fact, in just 19 games Herrera has already allowed eight homers, double his total from 2012. The Royals will hope that a stint in the minors helps their young reliever relocate his control.
Coleman, 27, has pitched extensively in the majors for the Royals over the past two seasons. Over 90 games, he has a 3.35 ERA along with phenomenal strikeout numbers. However, he too has suffered from high walk and home run rates.
He has been nothing short of phenomenal in the minors this season. Over 14 games, Coleman has allowed just three earend runs with 30 strikeouts in just over 26 innings.
Coleman will be in uniform and available for Thursday's game against the Angels.