Phillies: How does Jake Arrieta signing affect 2018 projections?
By John Town

How much does signing Jake Arrieta affect the Phillies’ projections for the 2018 season? Is it enough to get to the playoffs?
The Phillies finally got their man Sunday night, reportedly signing 2015 NL Cy Young winner Jake Arrieta to a three-year contract. Bringing him in adds depth to a starting rotation that desperately needed it without burning the team in the long-term.
Worrying about the immediate future, how much of an impact does signing Arrieta make on Philadelphia’s 2018 projections?
Baseball Prospectus’s PECOTA system projects the Phillies to go 78-84 sans Arrieta, third in the National League East behind the Nationals and Mets. There would still be three teams ahead of them for the second wild-card spot. Their pitching staff is especially desolate as Aaron Nola is the only pitcher projected to have more than 1.5 wins above replacement.
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Averaging out PECOTA’s projections for 2018 puts Arrieta at a 3.92 ERA, 1.18 WHIP, and 2.1 wins above replacement. This puts him as the second-best pitcher on the team behind Nola. This would be a step back from last year, but projections are always somewhat conservative compared to the year prior.
A best-case projection for Arrieta from PECOTA still doesn’t quite match his Cy Young numbers from three years ago, but they are still great.
The 90th percentile of projections for Arrieta put him at a 2.99 ERA, 1.01 WHIP, and 4.1 wins above replacement.
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Meanwhile, the 10th percentile of projections give him far worse numbers compared to last year at 0.4 wins above replacement, a 4.88 ERA, and 1.37 WHIP.
Dan Szymborski’s ZiPS projection system projects Arrieta to post a 3.67 ERA, 3.98 fielding-independent pitching, 2.82 strikeout-to-walk ratio, and 2.7 wins above replacement. These numbers are more in line with his stats from last year.
Arrieta is projected to accrue somewhere between two and three wins above replacement. This would get Philadelphia around .500 with 80 or 81 wins.
It would be a huge step in the rebuilding process for the team to break even in the standings, but there would still be several teams ahead of them for even the second wild-card spot.
Next: Phillies sign Arrieta: Winners and Losers
Signing Arrieta alone may not be enough to get Philadelphia a wild-card spot based on the projections. However, there is a strong chance that Arrieta and/or other players on the team outperform their projections. This would get them right on the precipice of a playoff spot this year.