General manager Neal Huntington characterized the acquisition as an opportunity to add competition to camp, though it also appears to be a sign that the Pirates aren't quite sold on the lefty options already here.
Olson joins a group of four lefties -- Scott Olsen, Joe Beimel, Brian Burres and Justin Thomas -- still in camp and under consideration for a spot in the bullpen. Of those four, only Olsen is already on the roster, and he has not pitched all that well since recovering from a hamstring strain.
"[Olson's] another guy we'll get an evaluation on in Spring Training," Huntington said. "It's a player that we have liked for a couple of years. Actually, we tried to acquire him when he was with Baltimore. I've tried a couple of times with Seattle. He came available on waivers, and we claimed him."
2010 Spring Training - null
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Olson had been in a deep competition for a left-handed role in the Mariners' bullpen this spring, but he had been outpitched early. In five Cactus League innings, Olson gave up seven hits and walked four.
Because Olson is out of options, the Mariners had to place the 27-year-old on waivers once they determined he would not make the Opening Day roster. His roster status means the Pirates would have to do the same if Olson doesn't win a spot in their bullpen by the end of Spring Training.
It also means that the Pirates will look at him solely for a relief role right now.
"I felt personally that, hey, I haven't shown yet what I can do," Olson said on Friday. "In no way am I going to put into a handful of innings how far I've come. I know there are still two weeks left. I feel great. I'm getting better each time out, and I know by Opening Day, I'll be ready to go."
Olson, who made his Major League debut with the Orioles in '07, has made 44 starts and appeared in another 55 games out of the bullpen. The lefty pitched exclusively out of the 'pen in 2010, finishing with a 4.54 ERA in a career-high 35 appearances. He didn't allow a run in 24 of those games, but Olson was knocked around for 42 hits in 37 2/3 innings.
Olson has also been prone to giving up home runs. In 283 Major League innings, Olson has served up 46 homers. His career ERA sits at 6.20.
"Probably why he is on waivers is they've seen something that concerns them," Huntington said, when asked specifically about the home run total. "From our standpoint, we see a guy who has a three-pitch mix that can come in here and have a chance to compete to help us."
Those three pitches include a fastball, slider and changeup.
It will be at least a few days before the Pirates will be able to evaluate Olson in a Grapefruit League game. Though he is expected to fly to Florida on Saturday, Olson needs to get back on a throwing program under the Pirates' supervision before the team pitches him in a game. Olson last pitched on Monday.
"[It's] just kind of the way things played out; it came sooner than I expected," Olson said of Seattle's decision. "But they made a decision based on what they needed, and I respect that. I'll just move forward now."
Though Huntington said he'd be comfortable going with seven right-handed relievers, it seems as if the Pirates' ideal scenario would be to have two lefties. None of the lefties seems to have solidified a spot yet.
Olsen, who just made his first appearance on Monday, seemed a strong candidate for the 'pen after falling behind in the rotation competition. But after allowing four earned runs, three walks and five hits in his first 2 1/3 innings, he still has much to prove.
Beimel was expected to be a shoo-in to serve as the team's late-inning left-hander, though he, too, has struggled. Sidelined early in March with forearm tightness, Beimel has been hit for four earned runs on seven hits in his two innings of relief.
Thomas came into camp as another bullpen candidate, though his chances of making the roster appear to be diminishing. Though he is healthy, Thomas has not pitched in a Grapefruit League game since March 12. Huntington confirmed that Thomas has been available as a backup, but the fact that he is not pitching suggests the Pirates aren't seriously considering him at this point.
Burres has pitched well over the past month, though the Pirates might prefer to let him start in Triple-A, so he could be available in case they need a spot starter. Burres showed last season that he can readily adapt to such a role.
In nine Grapefruit League innings, Burres has not allowed a run. He has given up five hits and four walks, with all of those free passes coming in one three-inning outing.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.