Moving On Up: Edwin Diaz

About a month ago, the Mariners elicited some second-guessing when it was announced that Edwin Diaz - the team's top pitching prospect - would be shifting to the bullpen. Lookout Landing offered a pragmatic take on the move, pointing out that it could merely be a means to get him to the Majors more quickly, and reminding everyone that nothing in necessarily permanent. Before delving further into the transition and what Diaz offers, let's take a look back at what I wrote about the 22-year-old in our top-ten Mariners prospects list:

If you were to take Edwin Diaz's stats at face value, you would likely be unimpressed due to a middle-of-the-road walk rate and the 4.57 ERA at Double-A. This is a textbook example of the perils of scouting the stat line, however, as most every scouting report indicates that Diaz improved his change-up and command markedly over previous seasons. Diaz's arsenal consists of a low-to-mid 90s fastball, a slightly above-average slider, and a solid change-up, and he has all the makings of a mid-rotation starter.

In his return trip to Double-A, Diaz looked every bit the starting pitching prospect that his stuff suggested (albeit in only six starts), pitching to the following line - 29.0 IP, 29 H, 5 BB, 38 K, 3.10 ERA, 55% GB. It was a small sample size, to be sure, but Diaz looked terrific. And then he moved to the bullpen, where he has been predictably stellar. In 10 appearances as a reliever, Diaz has tossed 11.2 IP, allowing only 3 H and 2 BB, striking out 16. He has allowed just one run (unearned), and maintained a 61% groundball rate.

A move to the bullpen was always in the cards for Diaz, due to his slight build and middling change-up, and his stuff tended to sag as games wore on. Since moving to relief, his fastball has sat in the upper-90s, and his slider has shown more bite. When those pitches are only, both are legitimate plus offerings. Diaz has also all but abandoned his change, as is often the case with relievers, so it will be interesting to see how he is utilized going forward. If the plan is to have him shift back into the rotation at some point, we should see Diaz sprinkle in the change-up every so often as Aaron Sanchez did last year. And, as was the case with Sanchez, Mariners fans should be hoping that that is the case.

In the short-term, Diaz should be a tremendous asset to the Mariners already strong bullpen. He is essentially replacing the struggling Joel Peralta, so he stands to pick up a good number of innings in middle relief. However, his value may be limited in fantasy leagues due to the presence of solid closer Steve Cishek, and the incredibly effective trifecta of Nick Vincent, Mike Montgomery, and Vidal Nuno. The team is not necessarily beholden to any of these relievers, but a team in the midst of contention isn't likely to fix what isn't broken.

I do think Diaz is here to stay, and his ability to rack up strikeouts and limit hits and walks will make him useful in deeper leagues. For the time being, though, saves are not in the cards. And, in the long-term, enjoy seeing the best stuff in the Mariners system.