Age on Opening Day 2016: 24
How acquired: Trade with Rays, Feb. 2014
2015 stats: 49 G, 48.1 IP, 2.79 ERA, 2.64 FIP, 43 SO, 11 BB, 0.952 WHIP, 15 R, 15 ER, 2-1, 2 HR, 145 ERA+, 8.0 SO/9, 3.91 SO/BB
2016 storyline: The 2015 season for the Nationals will be looked back on as an overall disappointment, a year that some would go further to describe as an abject disaster. But one of the more pleasant surprises that came out of that fateful season for the Nats was the emergence of reliever Felipe Rivero.
Rivero debuted in April and became one of the lone bright spots for a Nats bullpen that was otherwise a glaring weakness for most of the season. He ended up posting a 2.79 ERA in 49 appearances and acquitted himself nicely as a rookie, standing out with a high-90s fastball coming in from the left side.
This upcoming season for Rivero will be about proving that 2015 was no fluke, that he can pitch clean innings now that there is plenty of tape out there on him. How will he adjust to the adjustments made by hitters? The answer to that question could determine a lot for the Nats' bullpen this season.
Best-case scenario: Rivero was excellent for a rookie and his peripheral numbers suggest he could get even better moving forward. He kept runners off base with a 0.952 WHIP, held a 2.64 FIP and struck out eight batters per nine innings. If he can improve his slider and get better at commanding his fastball, he should strike out even more than the 43 whiffs he got in 48 1/3 innings this past season.
Another level for Rivero could turn him into a real asset for Dusty Baker. There is definitely room this year for Rivero to lock down a late-innings role as the setup man, or maybe even at closer depending on the future and performance of Jonathan Papelbon.
Worst-case scenario: Plenty of relievers - and starters for that matter - have looked great early in their careers before adjustments made by opposing batters rendered them ineffective. It happens all the time and it could happen to Rivero.
A worst-case scenario for Rivero might look a little like Aaron Barrett's 2015 season. Barrett was very good in 2014, but couldn't regain that form in his second year. Injuries played a significant role, but his struggles really hurt the Nationals' bullpen, as they were counting on him to take another step in his development and become a big piece of their relief corps. Rivero will hope to avoid following a similar path this season.
Most-likely scenario: Interestingly enough, both FanGraphs and Baseball Reference are skeptical of Rivero in their projections, each predicting him to take a notable step backwards in 2016. Both sites predict him to walk a lot more batters and see his ERA rise by nearly a full run.
That may or may not be going to far, but it is reasonable to expect Rivero to regress slightly in 2016. Opposing batters will now know what to expect, particularly those who saw him plenty in the NL East, and Rivero will likely be asked to pitch in more high leverage situations now with Drew Storen gone. He looked ready for a larger role by the end of the 2015 season. We'll find out if that's indeed the case.