"It's not just having a second lefty," Francona said last month while in Cleveland for Tribe Fest. "It's having one you can depend on."
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Logan, who agreed to a $5.5 million base salary for 2017 with a $7 million option (or $1 million buyout) for 2018, has been one of the more dependable lefty-on-lefty relievers in the game in recent years.
Whereas Miller is used as a versatile leverage weapon -- lefty and righty splits do not apply -- Logan has found his niche as an effective left-handed specialist. Over the course of 11 seasons in the Majors, he has limited lefty batters to a .233 average. Over the past two years, left-handed hitters have posted a .175 average off him. The average dropped to .142 for the 2016 season, which was Logan's third with the Rockies.
"What we tried to do is find the right guy to complement our bullpen," said Chris Antonetti, the Indians president of baseball operations. "We weren't just going to sign a guy because he was left-handed. In fact, we wanted to try to identify pitchers who we thought could help us. Boone, we feel, is that guy."
In the past two seasons combined, Logan has ranked as one of the Majors' best lefty relievers against left-handed batters. Among southpaws with at least 150 opponents' at-bats against lefty hitters, Logan ranked second in strikeouts (70), third in average (.175), fifth in slugging (.254), and sixth in on-base percentage (.276) and OPS (.530) for the 2015-16 campaigns.
During that two-year period, Logan posted a 34.5 percent strikeout rate against left-handed batters. He has averaged 9.6 strikeouts per nine innings over the course of his career overall, and that rate has climbed to 11.2 over the past five seasons combined.
In 66 appearances last season for Colorado, Logan recorded a 3.69 ERA, with 57 strikeouts against 20 walks, in 46 1/3 innings.
As things stand, Logan will join Miller in a bullpen that also projects to include right-handers Cody Allen, Bryan Shaw, Dan Otero and Zach McAllister. That would presumably leave one bullpen job (unless Francona goes with an eight-man bullpen) with a long list of names in the running. Candidates include Cody Anderson, Shawn Armstrong, Mike Clevinger, Kyle Crockett and Perci Garner, among many others.
"We feel we have a lot of quality alternatives," Antonetti said, "to both compete for the remaining spot or spots, and then as we all know, it's exceedingly important for us too have very good depth options that we can turn to throughout the course of the year. We know that there will be some evolution and some turnover in our bullpen throughout the course of the season, and we need to be prepared to weather that.
"We feel we have a really good group of guys that can support us, not only for the Opening Day roster, but for the balance of the season."
Last season, Cleveland's left-handed relievers posted a .245 opponents' average against lefty batters on the year. Remove Miller, and that average rose to .280 between the relief work of Ross Detwiler, Tom Gorzelanny, TJ House, Ryan Merritt, Shawn Morimando and Crockett.
"Having a second [lefty] would be great," Francona said. "But it also has to be a guy that can do what's asked when asked. In a perfect world, you have one, because then you potentially let Andrew not get up as much."
In order to add Logan to the 40-man roster, Cleveland designated right-hander Austin Adams for assignment, giving the team 10 days to either trade or release him, or outright him to the Minors if he clears waivers.