Like a fat kid stealing from a summer camp’s tuck shop and stashing his forbidden calorie increase where the counselors can’t find it, the Oakland A’s are quietly amassing one of the best bullpens in baseball.  As teams like the Yankees and Red Sox invest in expensive treats like Rafael Soriano and Bobby Jenks (who knows tuck shops better than most), the A’s are relying on a combination of young, in-house talent (home made candy if you’re interested in ill-advisedly extending this metaphor even further) and shrewd pick ups to form situational nightmares for opposing teams in late innings.

Coming into the offseason, the Athletics already possessed one of the better young bullpens in the league, and since Friday they’ve added both the extremely underrated Grant Balfour and now, veteran lefty Brian Fuentes to two year contracts.

Take a look at these numbers from last season.

Brian Fuentes vs. left handed batters: 1.79 FIP, 0.71 WHIP, .132 AVG, 11.57 K/9, 4.50 K/BB.
Craig Breslow vs. left handed batters: 3.50 FIP, 0.96 WHIP, .188 AVG, 9.00 K/9, 3.25 K/BB.

Grant Balfour vs. right handed batters: 2.68 FIP, 0.87 WHIP, .172 AVG, 9.19 K/9, 3.67 K/BB.
Joey Devine vs. right handed batters: 1.34 FIP, 0.66 WHIP, .125 AVG, 11.52 K/9, 5.00 K/BB.
Brad Ziegler vs. right handed batters: 2.70 FIP, 1.01 WHIP, .215 AVG, 7.15 K/9, 3.27 K/BB.

And of course, let’s not forget about the team’s 26 year old closer Andrew Bailey, who over the course of the last two seasons has put together a 2.70 FIP, 0.91 WHIP, .182 AVG, 9.05 K/9, 3.59 K/BB against all batters.

Oakland’s pitching staff last year gave up the fewest runs in the American League.  And after only losing an ineffective Ben Sheets, a barely there Justin Duchsherer and Vin Mazzaro this offseason, while adding reclamation projects Rich Harden and Brandon McCarthy in addition to the two relievers, it’s hard to imagine anything changing.

Of course the team still has to score runs, and despite once again missing out on Adrian Beltre, Oakland still attained the biggest offensive upgrades in the AL West this offseason with Hideki Matsui and Josh Willingham adding actual power to a previously impotent lineup David DeJesus will also improve.

While it may not have been their first plan, through the Athletics’ surprisingly successful offseason and a disastrous one for their neighbours in Los Angeles, Oakland will enter the 2011 season as the Rangers’ biggest rival.