With “Big Z” Brad Ziegler setting scoreless-innings-pitched records for the A’s and “Little z” Jeff Samardzija picking up a save for the Cubs, there has been some swirling speculation about the future relief prospects for these two. What are their likely bullpen roles, and are their skills worth adding to a fantasy team?

(above, Ziegler serves up a submarine sandwich for the Royals yesterday)

To start with Brad Ziegler: since arriving in the majors on May 30, he has put together a historic run of consecutive scoreless innings, 30 through last night, causing some now to envision a consistent set-up role for this 28-year old to pave the way for closer Huston Street. The current information about trade rumors around Street says that there don’t seem to be any impending deals for him, so if that holds through the rest of the day, it seems likely that Street will remain the A’s closer through the rest of the year. That puts Ziegler in a mix that includes Alan Embree, Keith Foulke, Joey Devine, and Santiago Casilla for the set-up role.

Ziegler’s stat line in the majors this year include some very fun numbers (the 0.00 ERA and 100% strand rate chief among them), along with some disturbing ones (his low 4.20 K/9 and luck-heavy .203 BABIP). What has worked extremely well in Ziegler’s favor is his 72.2% groundball rate, the highest of any reliever who has pitched 30 innings. With his sidearm delivery, he almost exclusively throws a fastball (nearly 90% of his pitches, according to Pitch F/X), which apparently is good enough to induce all those grounders.

So should he be added to your team? The first thing to note, of course, is that he will give up runs eventually, and come back down to earth with his strand rate. THT puts his xFIP at 3.38, which is likely a reflection of his low strikeout rate (and combined 2.10 BB/9 rate), so he could come back down to a rather low mark. However, his groundball-inducing skill is excellent, and could very well be skill more than luck: in 24.1 innings in AAA Sacramento this year, he pitched into a 68.7% ground ball rate; through AA and AAA in 2007, and that AAA time in 2008, he put together 102.2 innings without giving up a single home run.

Going forward, it looks like Ziegler will share time with Santiago Casilla as the main set-up pitchers for Street, especially with Foulke and Devine dealing with injuries, and Embree suffering a 4.99 ERA. In leagues where having a good set-up pitcher is valuable, either seems a good option, though Casilla, who put together his own 16.1 scoreless-inning streak at the start of the season, seems better for a few reasons: his strikeouts (a 9.10 K/9 rate), strand rate (87.6%), and somewhat better xFIP (3.11).

As for Samardzija, he comes to the Cubs bullpen with a lot of opportunity for work. Kerry Wood is still out for the time being, and someone else needs to step in when Carlos Marmol needs a rest (Bob Howry tried for a bit, but his July ERA has been 7.30). Samardzija’s first save came on Sunday, when he retired all six batters he faced and struck out three. Samardzija burned up the minor leagues this year, retiring batters in AAA at a 9.64 K/9 rate. However, if you include his stats from AA this year, he’s posted a 6.46 K/9 rate (in fact, it’s his very recent performance that is boosting the rate: Samardzija had a 10.87 K/9 in his last month in AAA). Last year, his K/9 was 5.21 in AA, and it was 5.24 the year before.

To go with these strikeouts, Samardzija posted a 41.3% groundball rate in the minors this year. That doesn’t bode well for the likely decline in his strikeout rate in the majors, as he’ll have line drives and fly balls to contend with once hitters start making more contact, which could be disastrous for a reliever. So while Samardzija has done well for himself in his brief major league career thus far, and may get a few more save opportunities, fantasy owners would do well to be cautious in adding him to their teams.