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Because the margin for error is so slim, it's always hard to tell when the bottom is falling out for a baseball player. The difference between success and failure for a pitcher can be a handful of balls thrown six inches higher than expected, which makes it pretty tough to make grand pronouncements.

There are usually some warning signs, however, especially as a pitcher gets older. Diminished velocity is the surest sign that things are starting to go off the rails, but it isn't the only one. A drop in ground ball rate (and subsequent rise in home run rate), a change in pitch usage or a loss of command can all be signs that a pitcher is starting to lose it.

With a 6.98 ERA through Wednesday's action, it seems as if Mariners closer Fernando Rodney is starting to lose it. And yet, if you look under the hood at his numbers, the typical warning signs aren't there.

Sure, his K/9 has dropped a tad, to 8.4 per nine, but everything else seems fine. His groundball rate is nearly identical to last year's mark, his pitch selection looks the same, and even at the age of 39 his velocity remains elite. According to PITCHf/x, the proportion of pitches thrown in the strike zone compared to last season has only risen 0.6 percent, and his swinging strike rate has also gone up.

And yet, that ERA still sits there like a glaring red sign. And his strikeout rate has plummeted from 26.6 percent to 19.8 percent, so it's not all ERA. Rodney is, for whatever reason, getting worse results despite a lot of the underlying signs looking the same.

The interesting thing to note is that Rodney's changeup has actually been the biggest culprit for his struggles. He has mostly managed to survive as a two-pitch pitcher thanks to a dynamite fastball-changeup combination, but the changeup has really been the weapon. For his career, opposing hitters are hitting just .183 with a .122 ISO against his changeup. Those numbers are up to .261 and .348, respectively, with two of his three home runs allowed coming against the changeup.

He is still generating a ton of arm-side run with the changeup, per BrooksBaseball, and is throwing it right at the same velocity as he did a year ago. He is still generating a ton of swinging strikes -- 19.7 percent of his changeups end up in the catcher's mitt despite the hitter's best effort -- and is picking up groundballs slightly more often with the pitch than he did last season.

We often search for meaning in the numbers, assuming any outcome has to have an explanation that can be divined if we just dig far enough. However, Rodney looks like basically the same pitcher we saw a year ago in so many ways. He is having trouble putting hitters away -- 23.8 percent swinging strike rate with two strikes last season, compared to 19.7 percent this season -- but looks nearly identical to who he was last season otherwise.

And this is why it's so tough to say what is wrong with Rodney. He is at the age where it wouldn't be terribly surprising if he just kind of lost it, but you would expect there to be glaring, obvious warning signs. However, it is possible that the margin for error was so slim, any dip could prove catastrophic.

The good news for Rodney's Fantasy owners is it's hard to see him losing this job. One potential usurper, Danny Farquhar, was so bad he earned a trip back to the minors this week. The 25-year-old Carson Smith has an 0.61 ERA since joining the Mariners last season, but has just 29 1/3 innings under his belt in the majors, so the team might want to see more out of him before throwing him into the role.

Smith is probably the best option if you are looking for someone to add and stash in the event Rodney continues to falter. However, Rodney's track record will probably buy him more time, especially with no glaring physical issues holding him back at this time. The Mariners haven't made much noise about moving on from Rodney, with manager Lloyd McClendon even giving him a vote of confidence last weekend.

Fantasy owners may be tiring of the Fernando Rodney Experience, but that doesn't mean it's going away anytime soon. Until he actually loses the job, Rodney is probably still too valuable to drop.

Sean Doolittle, Athletics
Stock: Down

Fantasy owners who have been stashing Doolittle since the spring were probably hoping he would come back and jump right into a ninth-inning role, providing an immediate return on the investment. However, manager Bob Melvin told reporters Doolittle will be worked back into shape before being moved to the closer's role, so that is going to have to wait. Especially if Doolittle's reported diminished velocity from his rehab assignment remains. Doolittle might have pinpoint control, but that doesn't mean he was your stereotypical crafty lefty, getting by on guile. He lived in the mid-90s with a fastball that he relied on almost exclusively. However, he has reportedly been throwing closer to 90 mph since beginning his rehab assignment, making the 9.00 ERA he posted over five minor-league innings at least something of a concern. If he proves healthy, Doolittle should get the role back quickly and could be an elite option. However, there is at least some reason to be concerned about him right now.

Last week's stats: N/A

Shawn Tolleson, Rangers
Stock: Up

Last week in this space, I wrote that it was only a matter of time before Neftali Feliz would lose his job in the ninth inning, which turned out to be quite true. The club hasn't officially named Tolleson the closer, but he has five saves in the last week, which speaks louder than any pronouncement from a manager. Tolleson has allowed just one hit in his five save opportunities and now sports a 2.82 ERA with 30 strikeouts and only four walks over 22 1/3 innings of work on the season. His save total lately has been inflated by a hot streak for the team as a whole, but his success in the role is a nice sign either way. Tolleson probably won't be an elite closer, but he has been good enough that his ownership level of 43 percent is way too low. If you need saves, he's probably the best guy on the market right now.

Last week's stats: 5 IP, 6 K, 2 H, 1 BB, 0 R, 5 S

Brad Ziegler, Diamondbacks
Stock: Up

Entirely too much digital ink has been spilled over the last few weeks discussing a Diamondbacks team that, until a recent collapse by the Marlins, had the fewest saves in baseball. The biggest problem is how hard it has been to settle on one guy to target. First, it was Addison Reed. Then, Reed was to be supplanted by Ziegler. But hold on, here's Diamondbacks manager Chip Hale giving a sort of "nudge-nudge, wink-wink" endorsement of Enrique Burgos last week. Burgos' shoulder provided a final answer this week, as tendinitis in the joint landed him on the 15-day disabled list Tuesday. With Burgos out of the picture, Ziegler should have an unopposed path to the ninth inning, if the Diamondbacks can ever get there with a three-run lead. That hasn't happened too often and Ziegler isn't the kind of pitcher who can rack up the type of strikeout numbers that make him useful even when he isn't getting saves, so he isn't a must-add option even without opposition for the role.

Last week's stats: 2 2/3 IP, 3 K, 1 H, 1 BB, 0 R, 2 S