"Our scouts have seen him develop through the years from a projectable young arm as an amateur and Minor League prospect into a young, polished, strike-throwing Major League starting pitcher," Rangers pro scouting director Josh Boyd said. "He has plus makeup and work ethic that will only enhance his current rehab process."
Sampson, 25, made his Major League debut on June 18 against the Red Sox and allowed four runs on eight hits in 4 2/3 innings. He injured his flexor tendon warming up for his next start and ended up having season-ending surgery on June 30.
Sampson relies mainly on a fastball and slider with the occasional changeup. His fastball averages 91 mph.
A native of the Seattle area, Sampson was drafted by the Pirates in the fifth round of the 2012 MLB Draft out of Bellevue (Wash.) Community College. He was acquired by the Mariners on July 31 in a trade for pitcher J.A. Happ.
Sampson was 7-4 with a 3.25 ERA in 13 starts for Triple-A Tacoma before being called up by the Mariners. He averaged 6.8 strikeouts, 1.3 walks and 9.1 hits per nine innings for Tacoma.
T.R. Sullivan has covered the Rangers since 1989, and for MLB.com since 2006. Follow him on Twitter @Sullivan_Ranger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.