As of right now, three of the five mentioned players are on the 25-man roster. All three have shown so far that they can be great additions to the bullpen.
When you look at Keller, he has been extremely impressive. I did a write up on him early this month and things have not changed yet. During his time in the big leagues, he has now thrown 6.0 innings, allowing just one run. His ERA is 1.50 and he seems very composed every time he touches the mound. He does not strike out many batters, only striking out three.
However, coming from a guy who is 22-years-old and originally had only pitched as high as Double-A, what more could you ask right now?
The only question about Keller is whether or not he will continue to be a bullpen arm in the future, or if he will be moved to the rotation. Keller has always been a rotation arm, so being a bullpen arm is something new for him. Depending on what the Royals do at the trade deadline, Keller could find himself in the rotation at some point.
Hill is a great story. Hill was drafted in the 32nd round in 2014 by the Royals from Bacone College. Similar story to Keller, Hill had never pitched above Double-A in his career before getting the nod to join the big league team. Maria Torres of the Kansas City Star wrote a great story for how Hill found out.
During Spring Training, Hill threw 7.0 innings, allowed two runs (2.57 ERA) and struck out seven while walking two. He also only allowed four hits. Hill thought he was going to be optioned down, but obviously, that did not happen. He seems to be using that excitement and motivation to good use.
So far with the Royals, the 28-year-old submarine thrower has been nothing more than impressive. His 5.0 innings, posting a 1.80 ERA over six games is a great start for the rookie.
We all know who McCarthy is already. As anticipated, Maurer was optioned to Omaha, meaning someone had to fill his spot. Therefore, McCarthy who was thought to start the year with the Royals originally is getting his chance.
He made his MLB debut in 2016 but contributed more in 2017. Over his career, he has a 3.71 ERA over 53.1 innings and 42 games. In 2017 he pitched in 33 games, throwing 45.0 innings and posting a 3.20 ERA.
He has struggled so far this year, but the hope is that he can pick up where he was in 2017 and continue to improve. The 26-year-old has a chance of being a big part of the Royals bullpen, and with Maurer struggling this is the perfect opportunity for him to show he should stay up.