A look at the Sox's starting pitching depth

Mike Andrews is designer and developer of soxprospects.com and a special contributor to ESPNBoston.com.

For all the talk about the Red Sox having six starting pitchers for five slots, the new reality is that teams now stack their organizations with starting pitching depth, particularly the Red Sox. In the last five seasons, Boston has used an average of 11 starting pitchers per season, with an average of eight starters making at least five starts per year during that time period.

Last season, only four Sox starters made as many as 20 starts: Josh Beckett, Jon Lester, Tim Wakefield and Brad Penny combined for 109 starts. Seven other starters combined to make the other 53: Clay Buchholz (16), Daisuke Matsuzaka (12), John Smoltz (8), Justin Masterson (6), Paul Byrd (6), Junichi Tazawa (4), and Michael Bowden (1).

This season, the Sox head into April with six established starters: Beckett, Lester, John Lackey, Wakefield, Matsuzaka, and Buchholz. While it remains to be seen how Terry Francona will split up the starts between the six big guns, if history rings true we should expect to see the next group of pitchers on the depth chart. Even if that next group makes just 10 starts among them, those 10 games can be the difference in winning a division or clinching a playoff spot.

Here’s a look at that next group on the depth chart:

The Primary Options

Boof Bonser: Bonser was acquired from Minnesota in exchange for minor league reliever Chris Province back in December. A former first-round pick in 2000, Bonser was ranked as the 29th-best prospect in all of baseball by Baseball America in 2002. However, he never broke out above A-ball, and the right-hander struggled with weight issues throughout his career and later a torn labrum that required surgery, causing him to miss all of the 2009 season. Now coming in at 6-foot-4, 245 pounds, the 28-year-old seems slated to fill the long-man role in the Boston bullpen in 2010, and could remain stretched out to make a spot start if needed. While Bonser is probably not in Boston’s long-term rotation plans, he’s reportedly back to full strength from his shoulder surgery, getting his fastball back up to the 92-94-mph range and reincorporating his entire four-pitch arsenal. However, he hasn’t been overly impressive in three spring training games, going 0-1 with a 7.20 ERA and 5 strikeouts over 5 innings. Bonser is out of options, meaning he can’t be assigned to the minors without first clearing waivers.

Michael Bowden: A supplemental first-round pick in 2005, Bowden has been impressive at every level of the system despite regularly playing above his age level. In five minor league seasons, the right-hander has gone 33-25 with a 3.15 ERA and 477 strikeouts over 532 innings.

However, he’s had an up-and-down major league career early on. Exclusively a starter in the minor leagues, Bowden was primarily used as a reliever during a short stint with the big league club last season, and his overall 2009 results were poor (9.56 ERA and a 1.81 WHIP in 8 games). Coming into 2010, the 23-year-old has revamped his mechanics and added a slider, and the early results have been decent. Bowden should be Pawtucket’s opening day starter this season and is likely to be one of the primary options if Boston needs to call up a pitcher to make more than one start.

However, the young righty’s long-term future with the Sox may be as a reliever, especially as 2010 will be his last option year.

Junichi Tazawa: Tazawa is likely to start the season at the top of Pawtucket’s rotation and then be one of the first options if the Sox need to call up a starter. If the Sox have to decide between Bowden and Tazawa, the team may just go with whoever’s hot at the time or it could even come down to who’s scheduled to pitch on a certain day.

Tazawa has three option years left (he was signed out of Japan in December 2008), so the Sox have more time to decide whether the right-hander is better suited for the rotation or the bullpen. In 2009, Tazawa flashed some great numbers between Portland and Pawtucket, going 9-7 with a 2.55 ERA over 20 starts, but he was also inconsistent in the majors and ultimately had to be shut down in late September due to arm fatigue.

Still just 23, look for a stronger, more confident and more experienced Tazawa to emerge this April. To prove himself as a long-term rotation option, Tazawa will need to show greater endurance in 2010 and work on keeping the ball down in the zone.

The Emergency Options

Fabio Castro: Castro, 25, is a smallish left-hander with fringe stuff who nonetheless has managed to put up impressive numbers at both the minor league and major league levels throughout his career. In four organizations over seven seasons, Castro is 40-26 with a 3.52 ERA in 214 minor league games (61 starts), and 0-1 with a 3.30 ERA in 30 major league games (1 start). Already on the 40-man roster, the lefty is probably headed to Triple-A to start the season, but it’s unclear at this point whether he’ll start or relieve with the PawSox.

If he cracks Pawtucket’s starting rotation this season and continues putting up numbers in line with his historical stats, Castro may force himself into the discussion as a possible option if a starter is needed at the major league level.

Randor Bierd: Bierd is a tall right-hander with a low-90s fastball and an above-average change-up. He was acquired from Baltimore for David Pauley in January 2009. After spending the first half of the 2009 season on the disabled list, Bierd was mediocre in the second half with the PawSox, putting up a 4.55 ERA in 25 games (7 starts). While his stuff has looked good this spring, he struggled in two spring appearances with Boston. Nevertheless, the Sox appear committed to keeping the 26-year-old stretched out as a starter in Pawtucket this season. Heading into 2010, Bierd will need to make some strides if he’s going to be considered an emergency option for Boston.

The Prospects

Adam Mills: Mills was one of the best collegiate pitchers in the nation in 2007, going 14-1 with a 1.01 ERA and 141 strikeouts in 142 2/3innings for UNC-Charlotte, but he was largely written off by scouts as his fastball reached only the high 80s.

Boston took a flyer on him in the eighth round of the 2007 draft, and since then he’s quickly climbed through the Sox system, going 22-17 with a 3.93 ERA in 66 games spanned over stops in Lowell, Lancaster, Portland, and Pawtucket. Now 25, Mills relies mainly on control and deception, but he does it well. However, he’s yet to face major league competition in the regular season, and he got pounded in two appearances with the major league club this spring, giving up 9 earned runs and 12 hits in 3 innings.

Look for Mills to be a mainstay in the middle of Pawtucket’s rotation for the foreseeable future, with the chance for an emergency call-up at some point in the next year or two. The right-hander may also get a look this September if the Sox have the space to add him to the 40-man roster.

Felix Doubront: Doubront is a name to watch. Signed as a 16-year-old international free agent out of Venezuela in July 2004, Doubront has turned heads at every step up the ladder. The left-hander has gone 36-29 in five minor league seasons with a 3.74 ERA, which was tempered by a subpar 2007 campaign in which he struggled while rehabbing from a hernia operation. In 2009, Doubront went 8-6 with a 3.35 ERA, playing well above his age level as a 21-year-old in Double-A Portland.

As for 2010, Doubront appears to be on the bubble between a return to Portland’s rotation and a promotion to Pawtucket to start the season (he was optioned to Pawtucket on Friday, but that’s not always definitive as to initial placement). Pitching seven scoreless innings with the big club this spring while giving up only three hits certainly has helped his cause for a promotion to Triple-A.

Either way, he should see some time with Boston as a 40-man call-up this September. He’ll need to work on control and his pitch efficiency in 2010, and over the long term the hope is that he packs on some muscle to his frame in order to increase the velocity of his fastball a few ticks. If he can show refinement in those areas, the Sox have the makings of a solid No. 3 to No. 4 starter on their hands a few years down the road.

Casey Kelly: While Kelly is the only pitcher in the system that has demonstrated true ace potential, keep in mind that he is just 20 and that he has pitched in only 17 games as a professional. Most of us know the story by now -- Kelly was drafted as a pitcher/shortstop in the first round of the 2008 draft, and then spent his first pro season in 2008 as a shortstop. He then pitched for the first half of the 2009 season, dominating with Low-A Greenville and High-A Salem to the tune of a 2.08 ERA and 0.85 WHIP in 17 starts. He returned to play short for the second half of the season and in the Arizona Fall League, putting up mediocre offensive numbers, leading to a decision this past off-season to concentrate on pitching full-time.

Despite the lack of pro experience, Kelly's pitching skills are quite advanced, mixing in three plus pitches: a low-90s fastball, a hard 12-6 curveball, and a nice change, all with pinpoint control and a mature approach. The right-hander is slated to start the season with Double-A Portland in 2010, and he is likely to spend most of the minor league season with the Sea Dogs absent some unprecedented dominance. That being said, Kelly could get a call-up to Boston this September to get some major league exposure, and that would be quite an accomplishment, as the Sox have never called up a 20-year-old in the Theo Epstein era.

Ultimately, the Sox already have four established starting pitchers locked up for the next several years in Lackey, Lester, Matsuzaka, and Buchholz, and may be on the verge of locking up Beckett long-term as well. While that doesn’t leave a lot of room for prospects to break in, look for Kelly to make a bid for a spot in the rotation by mid-2011, but he’ll certainly have some competition from Bowden, Tazawa, Doubront, and Mills.