Series preview: San Francisco Giants a strong team, but rotation is vulnerable

After a four-game set in San Diego, the Pirates' road trip continues in San Francisco on Sunday. Here's what to expect from the 30-22 Giants.

POSITION PLAYERS: .272/.333/.407. 10.2 fWAR, second in National League. The Giants' great showing so far this season has been buoyed by performances by infielders Brandon Crawford (.299/.371/.506) and Joe Panik (.300/.373/.450) that don't look likely to continue. But there's no arguing that Giants position players have been terrific -- they've been among the National League's best despite getting little from Hunter Pence and a terrible season from the recently demoted Casey McGehee. (Matt Duffy currently occupies third base.)

Buster Posey (.295/.369/.460) is in the midst of another strong season, and first baseman Brandon Belt (.306/.383/.544), always a good hitter, could be off to the start of a career year at age 27. Left fielder Nori Aoki has been a great addition, with a .382 OBP so far, and Angel Pagan has had a strong year alongside him. The Giants have a .272 batting average as a team right now, and I suspect that will come down a bit -- the only NL team last year with a batting average that high was the Rockies. But they can regress a bit from where they are and still be effective.

PITCHING: 3.71 ERA, 4.00 FIP, 3.94 xFIP. 2.2 fWAR, 12th in the National League. Fortunately, the Pirates will dodge 2015 playoff hero Madison Bumgarner, and will instead face Ryan Vogelsong on Monday, Chris Heston on Tuesday and Tim Hudson on Wednesday. This relatively weak rotation draw represents a good opportunity for the Bucs.

Vogelsong's history remains baffling to me as a Pirates fan -- he pitched parts of five seasons for the Bucs and was mostly terrible, then headed to Japan for several years before returning to San Francisco as a 33-year-old and getting great results. Whatever was working for him in 2011 really doesn't anymore, but he remains a decent back-end guy despite subpar stuff. Heston is only in the rotation because Matt Cain is hurt, but he's pitched reasonably well so far this season, mostly because he limits walks and gets ground balls with his sinker. The 39-year-old Hudson is in the midst of his worst season since at least 2006, striking out just 4.3 batters per nine innings while throwing fastballs that have averaged just 88 MPH.

Between Vogelsong, Heston and Hudson, don't expect much velocity this week. Vogelsong and Heston are decent rotation options, and I wouldn't be surprised if the Giants, who generally get a lot out of players analysts underestimate, got more out of Heston than you'd expect. But a contending team should hope to have maybe one pitcher in its rotation like the trio the Pirates will face this series, not three.

The Giants' bullpen hasn't been anything to write home about, either. Its top performers, at least as far as peripherals are concerned, have been Sergio Romo, Javier Lopez and former Pirates prospect Hunter Strickland. Lopez is a lefty specialist who pitches sparingly. Strickland is more interesting, as the Giants appear to be starting to trust him again after he allowed homer after homer in a series of high-profile meltdowns in the postseason last year -- he's gotten holds in his last three outings. He now has 14.1 career regular-season innings under his belt, though, and he has 17 strikeouts and no walks. He also throws in the high 90s and dominated in Triple-A earlier this season.

On the other side of the ledger, lefty Jeremy Affeldt has had a disastrous season, and Jean Machi (another former Pirates minor-leaguer) hasn't been much better. Closer Santiago Casilla has a good ERA, but has had control problems.

OUTLOOK: This is still a very good team, but injuries to its pitching staff make it vulnerable. A healthy Matt Cain (and, to a lesser extent, Jake Peavy) would have made a difference to the Giants, and it's hard to see them as an elite team given its pitching staff. Even Tim Lincecum's resurgent season is a mirage -- he has a 3.00 ERA, but his xFIP is the worst of his career.

Nonetheless, the Giants' core of position players is terrific, and they should be able to balance some regression from their top hitters by getting more from Pence. They already have a fairly strong grip on the top Wild Card spot, and they appear fairly likely to make the playoffs. FanGraphs' projected standings lists the top six teams as NL clubs. The Dodgers, Nationals and Cardinals are, obviously, good bets to win their divisions (although only the Cardinals have established much distance between their nearest competitors at this point). But FanGraphs sees the Pirates finishing 87-75 and the Giants and Cubs finishing 86-76. (That suggests that the Pirates are somewhat better than their current record and the Giants somewhat worse than theirs, which makes sense to me.) That scenario, or something like it, could set up a Giants/Pirates Wild Card rematch at PNC Park.