Right-hander Dylan Thompson, the Mariners' 22nd-ranked prospect according to MLBPipeline.com, along with first baseman/outfielder Dalton Kelly and right-hander Andrew Kittredge, join the Tampa Bay organization.
Seattle drafted Thompson in the fourth round of the 2015 Draft out of Socastee High School in Myrtle Beach, S.C. The 20-year-old pitched well in his first taste of professional baseball, posting a 2.36 ERA in nine appearances (five starts) in the Arizona Rookie League in 2015. His 2016 campaign was cut short by injuries, however, and he posted a 5.79 ERA in three appearances (one start). According to MLBPipeline.com, he's now 30th among Rays prospects.
Kelly was selected in the 38th round of the 2015 draft by Seattle out of the University of California-Santa Barbara. At Low-A Clinton this season, he hit .293/.384/.416 with 30 doubles, seven home runs, 58 RBIs and 21 stolen bases in 130 games.
Kittredge, 27, has spent six seasons in the Minors after the Mariners drafted him in the 45th round in 2008 out of the University of Washington. Between Double-A Jackson and Triple-A Tacoma in 2016, the right-hander posted a 3.50 ERA in 37 appearances (five starts); he struck out 84 and walked 19 in 72 innings, including 47 strikeouts in 38 innings at Triple-A.
Shaffer was the Rays' No. 20 prospect per MLBPipeline.com. The 25-year-old corner infielder and outfielder hit .250/.315/.438 with six doubles, a home run and four RBIs in 20 games for the Rays this season. In 119 games at Triple-A Durham in 2016, he hit .227/.329/.367 with 11 home runs and 48 RBIs. He's now the 16th top Mariners prospect, according to MLBPipeline.com.
Motter, 27, played in 33 games for Tampa Bay in 2016, batting .188/.290/.300 with two home runs and nine RBIs. Also versatile defensively, Motter can play shortstop and third base, as well as in the outfield. In 88 games at Durham this season, he hit .229/.297/.389 with 13 homers, 46 RBIs and 19 stolen bases.
In addition to the trade with the Mariners, the Rays added eight players to the 40-man roster on Friday: right-handed pitchers Chih-Wei Hu, Austin Pruitt, Jaime Schultz, Ryne Stanek and Hunter Wood, left-handed pitcher Jose Alvarado and infielders Willy Adames and Daniel Robertson. Tampa Bay also designated right-hander Steve Geltz for assignment and released left-hander John Lamb.
Adames is the Rays' No. 1 prospect per MLBPipeline.com, and was the key return in the deal that sent David Price to Detroit at the Non-Waiver Trade Deadline in 2014. The 21-year-old shortstop out of the Dominican Republic hit .274/.372/.430 with 11 home runs and 57 RBIs in 132 games for Double-A Montgomery in 2016.
Others among Tampa Bay's top 30 prospects added to the 40-man roster are Hu (No. 6), Robertson (No. 10), Schultz (No. 11), Stanek (No. 12) and Wood (No. 18).
The moves bring the Rays' 40-man roster to full capacity.
Manny Randhawa is a reporter for MLB.com. Follow him on Twitter at @MannyRsports This story was not subject to the approval of Major League Baseball or its clubs.