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Programming note: This article is part of an ongoing feature series as Insider Joe Stiglich breaks down each A's position group over the offseason

The drama involving the A’s starting rotation began early last season and never really stopped.

Two key pitchers were lost to season-ending injuries in spring training. Unexpected heroes stepped up during the first half, and then two major trades involving the rotation became the talk of baseball leading into the second half.

As the main characters shifted and the plot twists continued, the overall numbers remained impressive, and that’s one storyline that didn’t stray from previous seasons. Oakland’s rotation led the American League with a 3.37 ERA -- the lowest figure by an A’s starting staff since the 1989 squad posted a 3.34 ERA during a World Series championship year.

But as we begin a position-by-position look at the A’s heading into the 2015 season, the starting rotation ranks as the most unsettled area of the team. Jon Lester, Jeff Samardzija and Jason Hammel -- the three starters acquired at midseason last year -- all are gone, leaving three openings in the rotation behind Sonny Gray and Scott Kazmir.

There’s no shortage of candidates to claim them. Seven -- yes, seven -- pitchers will show up to camp fighting for those three rotation spots. Throw in A.J. Griffin and Jarrod Parker, who the A’s hope can make healthy returns from Tommy John surgery, and that makes nine realistic options who can contribute in 2015 behind Gray and Kazmir.

STARRING CAST: Gray went 14-10 with a 3.08 ERA in his first full season in the majors. Twice he won AL Pitcher of the Month honors, when he posted a 1.76 ERA for March/April and a 1.03 mark in July. Yes, there were some bumps in the road -- he posted a 5.40 ERA over five June starts -- but Gray found a way to piece it back together. He was brilliant in a shutout of the Texas Rangers in game 162, which clinched a Wild Card berth for the A’s. He's the No. 1 starter heading into next season, and he’ll be looking to build on 2014, when he logged 219 innings over 33 starts.

Kazmir was terrific in the first half, posting a 2.38 ERA and making the All-Star team. In the second half, the lefty’s ERA rose to 5.42 and his WHIP went from 0.980 to 1.452. He turns 31 in January and should have plenty left in the tank, but Kazmir’s late-season struggles show how important it is to surround him with solid rotation depth.

CAMP COMPETITION: What a revelation Jesse Chavez was last season, assuming a starting role and posting a sub-3.00 ERA over the first three months. He moved to the bullpen after Lester was acquired July 31 and had begun to show signs of fatigue leading up to then. But Chavez now is a known quantity as a starter, and his performance last season makes him a natural candidate for the rotation in 2015, at least until Griffin and/or Parker return. Lefty Drew Pomeranz also merits a look, as he showed flashes of promise both as a starter and reliever.

But the real intrigue during spring training will involve several pitchers the A’s have acquired in offseason trades, and what impact they might have on the rotation. General manager Billy Beane said he expects both Kendall Graveman and lefty Sean Nolin, acquired from Toronto in the Josh Donaldson trade, to compete for starting spots. Graveman is particularly intriguing, a right-hander who spent four seasons at Mississippi State and jumped from Single-A all the way to the bigs during the course of the 2014 season.

Chris Bassitt, a right-hander acquired from the White Sox in the Samardzija trade, showed the A’s what he could do in September, when he limited them to one run over six-plus innings in a victory at US Cellular Field. He’s squarely in the mix for a rotation spot. Remember Brad Mills? The A’s re-signed the lefty to a minor league deal earlier this offseason, and he’ll get a look after making three midseason starts in Green and Gold last year.

Looking for a dark horse candidate? Arnold Leon, who got his first call-up last season but didn’t appear in a game, could force his way into the picture with a strong spring.

PAY ATTENTION TO: How well Griffin and Parker progress throughout the spring. Neither will break camp with the big club, but both will be looking to get through the spring with no major setbacks. If they can do that, it increases the chances they might be able to return before the All-Star break.