Jeffrey Flanagan of MLB.com provided details on the three players being sent to Kansas City:
Ken Rosenthal of the Athletic broke down each prospect:
Ken Rosenthal @Ken_Rosenthal
What #Royals get: Double A 3B Kelvin Gutierrez, who was on #Nationals’ 40-man; High A OF Blake Perkins, a former 2nd-rounder with good tools; RHP Yohanse Morel, a 17-year-old Dominican who has yet to play in U.S, but some Nats officials compare to the #WhiteSox’s Reynaldo Lopez.
Herrera has been one of MLB's most logical trade candidates for months given the Royals' descent into the American League Central cellar and his contract-year status.
His numbers have also been superb. In 25.2 innings this season, Herrera has logged a 1.05 ERA, 0.82 WHIP, 22 strikeouts and just two walks.
That efficiency has been buoyed by a stellar three-pitch arsenal that features a blazing fastball—which is still registering an average of 96.4 mph despite dropping a few ticks from his peak—nasty slider and steady changeup, according to FanGraphs. Herrera had spent his entire seven-plus year career in Kansas City.
Given those numbers and the short-term nature of the acquisition, it's no wonder the Nationals closed a deal with the Royals.
Washington is three games behind the Atlanta Braves in the National League East and is a middling 12th in the league in bullpen ERA, per ESPN.com. Steadying the bullpen behind a rotation featuring the likes of Max Scherzer, Gio Gonzalez and Stephen Strasburg (when healthy) makes the team all the more dangerous in the chase for October.
This is also a Nationals team that lost in the NL Division Series in four of the last six years, and adding a dangerous presence like Herrera to the back end of the bullpen will allow it to shorten critical postseason games and find more success at the most important time of the season.