Yonder Alonso changed his swing early in 2017 to hit the ball in the air more often and, with some help from the lively baseball, set career highs in several offensive categories. But a lot of that came from a great stretch in May when he hit 10 homers in 20 games.
The rest of the year, Alonso hit .256/.353/.435, a modest downgrade from what Cleveland got the past two years out of Carlos Santana, and a more believable baseline for a projection going forward, since Alonso's crazy May had no precedent in his career. The other hitch with Alonso is that he's a platoon player with no history of hitting left-handed pitching, so Cleveland has to get creative with its roster, perhaps buying Yandy Diaz a first baseman's glove and giving him some reps there in March to try to give Alonso -- who hit just .181/.263/.417 against southpaws in his breakout year -- a caddy when there's a lefty on the mound.
It's not an ideal fit, since Alonso is a fringy defender at first, and their DH spot is filled at the moment by Edwin Encarnacion, who can play first but you probably wouldn't want to see it. There's also the possibility that they'll make additional moves, such as trading Jason Kipnis to let Jose Ramirez move to second base, thus making Diaz (most likely) the starter at third, or even dealing Encarnacion if there's a team willing to overpay after missing out on the one big power bat in free agency, J.D. Martinez. Cleveland finished third in the AL in OBP and runs scored last year, but their current lineup for 2018 looks like it'll come in a bit below those marks.
Do platoon first basemen really cost $8 million a year and merit two-year deals? Alonso is better than Matt Adams, who signed earlier in the day with the Nationals on a one-year, $4 million pact, but I'm not sure if he's that much better to deserve twice the salary and the second guaranteed year. Adams is also a left-handed hitting first-base-only kind of guy, useless against lefties but with huge power against right-handers -- he out-slugged Alonso against righties in 2017. Alonso does get on base quite a bit more than Adams does, walking at twice the rate and showing patience even earlier in his career before his power surge, but Adams makes up for some of that gap with more power.
You don't win any prizes for signing a player to a better contract, of course, but I think the Nats did a bit better here with some bottom-fishing given Alonso's platoon issues and lack of any track record of power before 2017.