Brad Miller has long been considered a breakout candidate for both fans and front office personnel alike. He possesses tremendous bat speed that translates to very high exit velocities off the bat. The hard contact leads to 15-20 home run pop now, and as he hits his prime could become even more than that. His walk rate, at 9.5%, has improved in each of his years in the big leagues and was consistently over 11% in the minors. The combination of patience, power, and touch of speed (13 stolen bases in 2015) make him a potential offensive threat. While Seattle has seemingly given up on Miller at shortstop due to excess of errors, Tampa Bay is willing to give him another shot to play at a premium position, and advanced metrics like UZR still think of him as a slightly above average defender at short. The Mariners have also had him play outfield to increase versatility and usefulness, although he struggled mightily defensively. The Rays received a talented bat primed for breakout that they will need to figure out defensively, but as a lefty, offensively skilled middle infielder, the rewards could be huge. Even in 2014, his worst season so far in his young career, he has been able to change the game with his bat, speed, and glove with plays like these:
Danny Farquhar and Logan Morrison are two other pieces that fell out of Seattle's favor following mediocre 2015 campaigns. Farquhar was brilliant in 2014, with 10.3 K/9 and just 2.8 BB/9 for a strong 2.66 ERA that solidified the back end of the Mariners bullpen. However, he struggled to replicate that success. His fastball velocity dropped, and along with it his strikeout rate and effectiveness. His walks rose and so did the fly balls, leading to a career high in home runs given up. His ERA and FIP both went up, at 5.12 and 4.60, respectively. However, if there is any team that can reinvent relievers and make them good again, it's the Tampa Bay Rays and renowned pitching coach Jim Hickey. Morrison, a former top Marlins prospect, has yet to fully tap into the potential he once had, but now at age 28 he has settled in as a decent hitter who can provide some left handed power. Against right-handers, he hit well, with a .244/.323/.444 slash line and all 17 of his home runs, but he was abysmal against lefties, hitting just .190 with nonexistent power. He struggled defensively as well, but will likely provide the Rays with some pop to replace or play alongside incumbent James Loney.
Nate Karns, a big right hander with top-notch stuff, should slot in nicely in the Seattle rotation behind the likes of Felix Hernandez and James Paxton. He has a hard, 92-96 mph fastball that has good movement as well as a filthy knucke-curve and usable changeup. A big part of his success this season was mixing in all three of his pitches effectively instead of relying on the hard fastball, and it showed with his 3.67 ERA and an 8.9 K/9 that, if qualified, would rank 7th in the American League behind David Price. He had injury issues as a prospect in the Nationals system, but has semingly moved past that and his 6'3'' 230 lbs. frame should be durable for the Mariners this season. Here is a video of his first start as a Ray, using his fastball effectively to the tune of eight strikeouts.
C.J. Riefenhauser and Boog Powell are two prospects that could make an impact in Seattle in 2016. Powell is an on-base machine, drawing walks and spraying hits all around the field. After putting up very impressive numbers in the A's system in 2014, they dealt him to Tampa Bay, and he hit well in AA and AAA combined. Powell slashed .295/.385/.392, putting his elite on-base skills on display adding on to his solid defense. His biggest weakness however, is that despite his speed, he is not a very successful base-stealer. In 2014, he had a success rate of just 51.6% before improving ever so slightly to a 56.3%. He must tighten up his efficiency to become a base-running threat that will be respected by pitchers and catchers in the major leagues, but at the very least his bat and glove will carry him there. Riefenhauser is a left handed reliever who has struggled in his brief big league trials, but is deserving of a larger role going into next season. He has consistently posted strong strikeout rates in the minors, a testament to his above average slider that can put hitters away. His fastball only sits in the high 80's however, so expect him to be a solid LOOGY at best.
Here is a video of Boog Powell taking batting practice, courtesy of FanGraphs:
Overall, this was a balanced deal that filled holes on both rosters with young talent that were blocked in their original organizations. Trades like these are rare but could pay giant dividends for both teams if these players reach their full potentials.