When asked if he would take a hometown discount to remain in the Windy City, he simply said “No.”
Since joining the Chicago Cubs, Arrieta has a 42-13 record with a 2.15 ERA, striking out almost four times as many batters as he walks. With his prior club, the Baltimore Orioles, he was 20-25 with a 5.46 ERA and a 1.7 strikeout-to-walk ratio. This season he is 6-0, but his league-leading 1.13 ERA is lower than either his FIP (2.79), expected FIP (3.13) or SIERA (3.41) thinks it should be. As a result, Arrieta is expected to produce between 5.0 and 5.3 wins above replacement in 2016, lower than his 2015 campaign (7.3).
“That’s why starting pitching is so valuable,” said Arrieta. “There’s not many guys that can pitch at the top of the rotation floating around the league.”
But Arrieta will be 32 years old when he is eligible for free agency in 2018, and, according to work done by Bill Petti at Fangraphs, that would be well past the prime for a starting pitcher. In other words, by that time, we may have seen the best Arrieta has to offer. Strasburg, meanwhile, will turn 28 years old in July.
Looked at another way, the total wins above replacement produced by pitchers after they turn 26 years old declines rapidly as they are replaced by younger, better pitchers.
If we use 5.3 projected fWAR in 2016 as the start of an aging curve we can begin to assess Arrieta’s future value. Per Fangraphs, his 7.3 wins above replacement were worth $58.6 million on the open market, and a 5.3 fWAR in 2016 would be worth $42.4 million. To account for aging, we can reduce Arrieta’s wins above replacement by half a win each year, at the same time inflating the cost of a win in free agency by five percent per year. That pegs Arrieta’s value at $179.7 million over seven years. This same method projected Strasburg’s seven-year value at $150 million three months before he signed his extension. Setting Arrieta’s decline at sixth-tenths of a win share per year, which falls more in line with what we are seeing in baseball today, his value on a seven-year deal drops to $142.4 million.
When Arrieta hits the free agent market there is sure to be more than one team bidding for his services, but signing him to a top-dollar deal is a risk that isn’t worth taking.