Mike Rizzo is not afraid of a little risk. When he targets a player -- as he's done a few times as the Nationals' GM, whether it's Jayson Werth, Max Scherzer or now Patrick Corbin -- he's nearly always been willing to tack on the extra year or increase his bid by a small percentage to ensure he closes the deal. Corbin is just the latest such addition, and while his contract is long for any pitcher (reportedly six years, $140 million), he was the best free-agent starter available and he gives the Nats the biggest possible upgrade out there to their current roster.
Washington entered the offseason with three definite starters in Scherzer, Stephen Strasburg and Tanner Roark, with candidates for the last two spots but none of them great bets to be much more than replacement-level starters. Joe Ross has the most upside, having just returned from Tommy John surgery to at least show he still has his prior velocity, but he threw 35 total innings in pro ball in 2018 and wasn't very effective at any level. So while he might turn into the pitcher we once thought he'd be, there's no telling if or when it will happen or how much he might throw in 2019. Erick Fedde made 11 starts for the Nationals last year, but still doesn't have a solid weapon to get lefties out (they had a .378 OBP off him in 50 innings). If the Nats were still in development mode, I'd say throw those guys out there, maybe mixing in Austin Voth, and see what happens. But they're trying to win now and Corbin helps them do that.
Corbin is coming off a career year in just about every aspect of his game, just missing his career high in innings, coming in at 4.8 rWAR (Baseball-Reference) and 6.3 fWAR (Fangraphs), thanks to career-best strikeout, walk and home run rates. His slider was the most valuable slider in the majors last year by Fangraphs' pitch values, and it generated three-quarters of Corbin's swings and misses in 2018. Not only is it sharp, but Corbin commanded the pitch last year, consistently hitting or going just beyond the corner low and away for left-handed batters, a big part of why he struck out a third of the lefties he faced last year. It was almost as effective against right-handers, a testament to the deception in his delivery and his command of the pitch.
The Nats lost a lot of value with Bryce Harper hitting free agency and the midseason trade of Gio Gonzalez, but they head into 2019 with a full year of Juan Soto, the arrival of prospect Victor Robles to take over center field, a brand-new catching tandem of Yan Gomes and Kurt Suzuki, and now the addition of Corbin to the rotation. They should have won 90-plus games last year, and didn't, so Rizzo just went out and increased their chances of doing so in 2019.
There's a catch, of course. Corbin gets six years at front-line starter money, but has pitched like a front-line starter for only two seasons in his career, and qualified for the ERA title only three times. He broke out in 2013, then missed 2014 due to Tommy John surgery. When he returned midway through 2015, the Diamondbacks treated him as if he'd never left and worked him hard in the second half of that season, which I still believe is the main reason he had the worst year of his career after that, with a 5.15 ERA in 155 innings in 2016.
The Nationals are paying Corbin to be the pitcher he was in 2013 and 2018, and they're asking him to do it more in the next six years than he's done it in the past six years. I interpret that as saying we want to win with Corbin in the next two years, while most of this core is together -- the other two starters, near-MVP Anthony Rendon, Trea Turner, Soto, Robles, Adam Eaton -- and damn the consequences if Corbin isn't as good in the back half of his contract. Washington has been too good for too long without any postseason success at all to show for it. The Nats are one of the only teams that can justify taking this kind of risk, assuming any team could justify it at all.