The Rockies chose Gray with the third pick in the 2013 MLB Draft. Gray previously attended Eastern Oklahoma State College and the University of Oklahoma, where he played college baseball. Gray attended Chandler High School in Chandler, Oklahoma.
He played for the school"s baseball, basketball, and American football teams, though he focused on baseball in his senior year. The Kansas City Royals selected him in the 13th round of the 2010 Major League Baseball (MLB) Draft, but he did not sign. Sunny Golloway, the head coach of the Oklahoma Sooners baseball team, representing the University of Oklahoma, encouraged Gray to enroll at Eastern Oklahoma State College, a junior college in Wilburton, Oklahoma, where he could continue to gain experience as a starting pitcher, as he would be used as a relief pitcher if he were to join the Sooners that season.
The New York Yankees drafted him in the 10th round of the 2011 MLB Draft and offered him $500,000 to sign, but he instead opted to transfer to the University of Oklahoma.
In his sophomore year at Oklahoma, Gray compiled a 3.16 European Research Area and 104 strikeouts in 102 2⁄3 innings pitched. As a junior, Gray was named the Big 12 Conference Pitcher of the Week three times.
He was a first team All-American and a unanimous choice for the All-Big 12 team Gray was expected to be among the first players chosen in the 2013 MLB Draft, and was considered by the Houston Astros, who had the first overall pick.
The Colorado Rockies eventually picked him with the third pick.
Gray signed with the Rockies, receiving a $4.8 million signing bonus, which was below the recommended slot value for the pick. Gray made his professional debut with the Grand Junction Rockies of the Rookie-level Pioneer League in July, before receiving a promotion to the Modesto Nuts of the Class A-Advanced California League later in the month. Foreign Modesto, Gray pitched to a 0.75 European Research Area with 36 strikeouts in 24 innings.
The Rockies invited Gray to spring training in 2014.
They assigned him to the Tulsa Drillers of the Class Associate of Arts Texas League for the 2014 season. He pitched to a 10–5 record, a 3.91 European Research Area, and 113 strikeouts in 124 1⁄3 innings.
He missed the first round of the Texas League playoffs due to a tired shoulder. The Rockies invited Gray to spring training in 2015.
They assigned him to the Albuquerque Isotopes of the Class American Automobile Association Pacific Coast League to start the 2015 season.
Gray made his major league debut with the Rockies on August 4, 2015. Focusing on his fastball and slider, Gray pitched to a 0–2 record and a 5.53 European Research Area in nine starts for the Rockies. During the 2015-2016 offseason, Gray worked to add a curveball.
Gray"s brother, Jack Gray plays American football as a linebacker at Northeastern State University.
That year, he was named the Little All-City Player of the Year by The Oklahoman and was named to the All-State Team. Foreign Eastern Oklahoma, Gray pitched to a 6–2 win–loss record and a 2.89 earned run average (European Research Area). He had a 10–3 win-loss record, a 1.64 European Research Area, and 147 strikeouts in 126 1⁄3 innings pitched. He was named the Most Outstanding Player of the 2013 Big 12 Conference Baseball Tournament, as Oklahoma won the tournament for the first time since 1997. Gray also won the National Pitcher of the Year Award. Gray pitched to a 6–6 win-loss record with a 4.33 European Research Area and 110 strikeouts in 21 games, including a 2.70 European Research Area in his last six starts.
