As a freshman with Butler, Mitchell appeared in 14 games for the Bulldogs with eight of those being starts. The left-hander threw 29 innings, in which he posted a record of 1-2 and struck out 21. Mitchell turned in his best start of the season at home against Northern Kentucky, where he went 4.2 innings and struck out five on April 21.

As a high school pitcher, Mitchell played in the Perfect Game Iowa Spring League as a senior in addition to being named to the Top Prospect Team. During both his sophomore and junior seasons, he led his high school team in strikeouts.