ANAHEIM -- How did they do it? How did the Angels, with 40 percent of the rotation in a constant state of flux, along with a bullpen that blew 25 saves, manage to lead the American League in earned run average last season at 3.57?

The easy answer is that Jered Weaver, Dan Haren, Ervin Santana and Scott Downs were lights out, making up for a lot of deficiencies.

The correct answer is more complex.

It never draws enough attention from the outside world, but the defense was a vital and valuable ally of the staff. Shortstop Erick Aybar won his first Rawlings Gold Glove, and center fielder Peter Bourjos and right fielder Torii Hunter were finalists for Gold Gloves along with Haren.

Defense is the one area of the game most difficult to quantify accurately. But the eye test told you that the Angels were as consistently efficient as any defense in the sport. Nothing breaks down a pitching staff the way a faulty defense can, and the leatherwork was top shelf across the diamond.

Ranked among the top 10 in the Majors at their positions by a panel of experts in the 2012 Bill James Handbook are catcher Jeff Mathis (fourth), first baseman Mark Trumbo (seventh), second baseman Howard Kendrick (eighth), third baseman Alberto Callaspo (tied for 10th), Bourjos (fifth) and Hunter (fourth). Ironically, Gold Glover Aybar didn't crack the top 10, and neither did left fielder Vernon Wells even though he was ranked second in Ultimate Zone Rating by Fangraphs.com.

The Angels' staff was more than the big three and Downs, the crafty lefty imported in free agency from Toronto. There were a number of unheralded athletes who stepped forward and delivered, even if it went generally unrecognized in the course of an 86-win season that left the club 10 games behind Texas in the American League West.

Jordan Walden, in just his second season as a reliever, made the AL All-Star team and nailed down 32 saves while blowing 10. He was imperfect, undone at times by a complicated delivery in need of constant fine-tuning, but his upside is tremendous.

You can't teach triple digits on the radar gun, and Walden gives you that along with a big breaking ball. He will work on commanding his changeup and becoming a more finished product, whether he retains the closer role or is pushed back into a setup job by a free agent or trade acquisition.

Hisanori Takahashi led the bullpen in innings with 68, and the highest percentage that were clean. He's seen as a lefty specialist, but the man from Japan actually was more effective against right-handed hitters (holding them to a .206 batting average) than lefties, who hit .261.

Takahashi, making 61 appearances, stranded 26 of 40 inherited baserunners. Downs stranded 25 of 35, putting together a staff-best 1.34 ERA in 60 games. Lefties hit .179 against Downs, righties .214.

Acquired to bring balance to the bullpen, Takahashi and Downs met the challenge.

Rich Thompson and Bobby Cassevah handled themselves capably in middle relief. Cassevah, with his hard sinker and slider, evolved into the seventh-inning man down the stretch and figures to get a shot at that role again in 2012.

Thompson was durable (54 innings) and effective, stranding 18 of 25 inherited runners with a 1.22 WHIP -- matching Takahashi's -- while holding hitters to a .224 batting average. Bringing the cutter into play with his four-seam fastball and big curveball enabled Thompson to keep hitters off stride from both sides of the plate. Lefties hit only .237 against him.

Cassevah's 1.18 WHIP was surpassed only by Downs' 1.01 among Angels relievers. He shut down right-handed hitters (.198) and held lefties to a .222 average, putting together a highly respectable 2.72 ERA.

Fernando Rodney's command struggles were exasperating, leading to Walden's early promotion to closer, but the free agent held right-handed hitters to a .180 batting average.

The Angels had anticipated quality work from Michael Kohn and Kevin Jepsen, power right-handers who have tasted success at the MLB level. But early command issues sent them to Triple-A Salt Lake, where they remained.

Kohn appeared to have found what was missing, but Jepsen underwent knee surgery, experiencing, in effect, a lost season.

As for the rotation, Angels manager Mike Scioscia has learned over recent seasons that five starters are not enough, repeatedly dipping into the system to replace injured arms.

If there are no imports, Jerome Williams, a late-season revelation, earned first crack at the No. 4 spot in the rotation. But the fifth slot looks wide open with Joel Pineiro in free agency and not expected to return. Right-hander Trevor Bell, who has moved back and forth from the bullpen to starting, is determined to make his pitch for that No. 5 opening along with Tyler Chatwood and Garrett Richards.

The Angels are exploring free agency, meeting with Texas ace C.J. Wilson, and a collection of less expensive starters are in the market.

Scioscia loves the raw stuff of Chatwood and Richards, but the young right-handers could use some time at Salt Lake to make refinements enabling them to pound the strike zone more consistently.

With the Angels, Chatwood was undermined by his 1.67 WHIP and 71 walks against 74 strikeouts in 142 innings. He frequently was on the borders of the strike zone without benefit of calls. With confidence and experience, he'll be rewarded for hitting the black corners.

Richards' talent is unquestioned. It's just a matter of putting it all together.

Perhaps more advanced than either Chatwood or Richards, but with less electric stuff, is Matt Shoemaker, the right-hander who was the club's Minor League Pitcher of the Year. He spent most of 2011 at Double-A Arkansas, making Salt Lake his likely destination. Shoemaker throws strikes and gets outs, always a good thing.