There’s been a lot of attention paid to the starting rotation’s struggles, and with good reason. Only Madison Bumgarner has been consistently effective through the Giants’ first 47 games. Barry Zito’s pitched well at AT&T Park, but has taken a beating on the road. Tim Lincecum’s showed flashes of brilliance. In his May 12 start against the Braves, he allowed only two hits and three walks over seven innings, and yielded no runs. He hadn’t pitched that well and that deep into a game since June 27, 2011 against the Dodgers July 14, 2012 against the Astros [Thanks to LOLKNBRCallers for pointing out my error]. Matt Cain appears to have righted the ship after a miserable April, but through his first ten starts, he’s given up nearly two home runs every nine innings pitched.

And then there’s Ryan Vogelsong. He hadn’t been right since the start of the season; his typical pinpoint command within the strike zone all but disappeared, along with his ability to get batters out. Just when it looked like he was turning the corner in Monday’s start against the Nationals — boom!  Broken pinkie bones on his pitching hand that will keep him sidelined through July.

The rotation’s overall ineffectiveness, unsurprisingly, has put a strain on the bullpen. But the bullpen’s had other problems aside from an increase in workload through the first quarter of the season, or perhaps because of it. Injuries have limited Jeremy Affeldt, who spent 18 days on the DL with an oblique strain, and Santiago Casilla, who’s now on the DL with a painful cyst in his right knee.

Simply put, the bullpen isn’t performing as well as expected.

Jeremy Affeldt SF GiantsLet’s start with Affeldt. He strained his right oblique muscle on April 15 and returned to action on May 3. Just before he landed on the DL, he pitched in a game against the Cubs, giving up a double and three walks in 1/3 of an inning. He blew the save and the Giants lost in extra innings. Perhaps he was already feeling the effects of oblique strain that day. Since coming off the DL, Affeldt’s yielded a .235/.297/.265 line to the 37 batters he’s faced. Still, for the season, Affeldt is sporting the lowest K/9 and the highest BB/9 of his career.

Of greatest concern is his fastball velocity; both his two-seam and four-seam fastballs are down more than 1 mph this season compared to last, and he’s relying them more. The velocity on his curveball is fine, but he’s throwing it much less frequently this year — 14.4% of his pitches vs. 27.1% in 2012. The  curveball is Affeldt’s out pitch. Perhaps he isn’t comfortable with his feel yet, or the oblique strain he suffered in April is affecting his ability to throw the pitch successfully. Either way, Affeldt’s been less effective without it.

Entering the season, manager Bruce Bochy planned to use Sergio Romo as his main closer, and that’s the way it’s played out so far. But Bochy relied on Affeldt to close on occasion last season even after Casilla developed a blister and Romo moved into the role. Affeldt has experience in high-leverage situations; even if Affeldt doesn’t like to close (as I reported back in February), he can do it successfully. But Affeldt’s oblique strain, his drop in velocity, and the strange disappearance of his curveball may give Bochy pause about using Affeldt if Romo is unavailable.

Javier Lopez SF GiantsWith Casilla on the DL, that leaves Javier Lopez as the other reliever with lots of experience in end-of-game high-leverage situations. Lopez had a bumpy start to the season — his spring training was shortened by a hand injury — but has pitched very well since mid-April. Lopez has extreme splits, however. Left-handed batters are hitting .212/.273/.255 off him vs. .333/.421/.500 for righties. Yes, we’re looking at a small sample size, but these splits are consistent over Lopez’s career. So Lopez can and has been quite effective when the opposing team sends several lefties in a row to the plate. But a lefty-righty-lefty-righty lineup can be trouble for Lopez.

The reliever some anticipated would be pushed into a higher profile role this season is George Kontos, but he’s been a bit of a disappointment so far. His strikeouts are down and his walks are up, leading to a 2.75 K/BB compared to 3.67 in 2012. As a right-hander, Kontos was more effective last season against right-handed batters, but his split was much less pronounced. In his (short) career, lefties have hit .253/.320/.433 off Kontos, but so far in 2013 that line is .419/.471/.839.

Bochy is likely familiar with these numbers. Kontos didn’t pitch at all in the series against the Nationals. The last time he pitched in a close game with the outcome in the balance was May 5 vs. the Dodgers. With the Giants leading 4-0 in the 8th inning, Kontos entered the game with one out and two men on base. He gave up a single and a walk and was lifted for Affeldt, who gave up consecutive singles. Three runs scored. Jean Machi got the final out. Kontos hasn’t seen a high-leverage situation since.

That leaves Machi, Jose Mijares, Chad Gaudin, and Sandy Rosario, who was recalled from Fresno after Casilla went on the DL. Machi’s been up and down to Triple-A several times so he’s seen limited action. He’s pitched well, but has little big-league experience. If Kontos continues to under perform, Machi is likely to gain that experience fast. Mijares is another lefty with a big platoon split, although he’s less effective than Lopez. Rosario’s kicked around the minors for years. He’s likely to see mop-up duty in games where the Giants are winning or losing by a large margin.

The big question is whether the Giants will slide Gaudin into a spot starter role to replace Vogelsong, at least in the short term. With the off day on Thursday, the Giants won’t need a starter until Tuesday’s game against the A’s. Lincecum will pitch Friday, Zito on Saturday, Cain on Sunday, and Bumgarner on Monday. They’ll need a fifth starter again for the June 2nd game against the Cardinals in St. Louis. The team then enjoys off days on June 3, June 6, and June 10, giving Bochy time to reshuffle the rotation and the bullpen.

One of Bochy’s managerial strengths is optimizing the performance of the bullpen. He will be put to the test over the next several weeks — if not longer — as bullpen roles shift as the team demands and performance warrants.