For the Boston Red Sox, this offseason has been quite momentous. They landed Adrian Gonzalez and Carl Crawford, the two best available offensive (and two of the best defensive) players.

But, when you take into account that the Red Sox still had one of the best offensives in baseball last season, and that both Adrian Beltre and Victor Martinez—one and two in terms of importance to the Red Sox offensively last season—the additions of Crawford and A-Gon might not have much of a short-term difference in the production the Red Sox see offensively.

Rather, the improvements made in the bullpen—namely the additions of Bobby Jenks and Dan Wheeler—will have the most impact. The Red Sox had the 12th lowest reliever ERA in the American League last season (4.24). While much was made up of Jonathan Papelbon’s struggles to nail down games, it was really the middle of the bullpen that performed the poorest.

Ramon Ramirez, who was lights out in 2009—2.84 ERA in 70 games and 69.2 innings of work—saw his ERA rise to 4.46 in 44 games and 42.1 innings of work last season. He went from being arguably the most consistent facet of the Red Sox ‘pen in 2009 to the least reliable in 2010. He was shipped to the Giants at the trading deadline for a minor leaguer.

Other noticeablely shoddy seasons came from Manny Delcarmen—4.70 ERA in 48 games—and Hidecki Okajima, whose ERA rose to a career high of 4.50. Delcarmen was sent to the Rockies via waivers in August, and Okajima remains a question mark coming into the 2011 season.

So when the Sox added Bobby Jenks and Dan Wheeler to the ‘pen for the 2011 season, they made a drastic improvement on their biggest weakness.

For analysis’ sake, I won’t delve much into Jenks’ value to the team. Long story short, he should help spell Daniel Bard, who appeared in 73 games and 74.2 innings of work. Both statistics were fourth highest among AL relievers.

I want to examine Dan Wheeler, probably the Red Sox who has gotten the least attention, but one who could end up having the most significant short-term impact. Despite the mark of guys like Gonzalez, Crawford and Jenks, Dan Wheeler will be the team’s biggest asset in the middle innings, which is where the Sox struggled the most in 2010.

Let’s start with the basics. For a good portion of his 11-year major league career, Wheeler has been one of the more reliable middle relievers in baseball. From 2004-06, Wheeler posted a 2.49 ERA in 160 games with the Houston Astros. After a rough 2007, which saw an ERA over 5.00 and a midseason trade from Houston to Tampa Bay, Wheeler posted a 3.24 ERA from 2008-10 in 203 appearances for the Rays.

So that being said, how will Dan Wheeler be used as a Red Sox? Certainly, he’ll be the guy who gets the call in the sixth and/or seventh inning. He’ll be the guy called on when a starter exits early, or when the Red Sox need an arm to get one guy out. His value as a middle reliever is already evident.

However, there’s another aspect of Wheeler’s game that I find intriguing. At least last year, Wheeler did exceptionally well in getting left handed batters out. Despite the fact that Wheeler is a right hander, and one with a fairly lackluster career average against left-handed batters (.275 opponent batting average; .833 OPS), Wheeler actually had better numbers last season against lefties than he did against righties. Lefties batted just .154 (as compared to .222 for RHB) with an OBP of .227 (as compared to .287 for RHB).

What accounts for this drastic change? Last season, Wheeler threw his slider 30 percent of the time, and his cutter 15 percent of the time. Both were highs for his career in Tampa Bay. He also threw his fastball just 47.5 percent of the time, a career low with the Rays. As a result, he gave up just three HRs to left-handed batters in 2010; he has been prone to giving up the long fly against lefties during his career.

It seems as if Wheeler made a conscious effort to keep the ball in the park last season and force weak contact. While this may have been the case, Wheeler was the beneficiary of an anemic .103 BABIP (batting average against balls in play) against left-handed batters last time. At the same time, his xFIP (expected fielding independent pitching), was a very high .472 against lefties last year.

Either way, the Red Sox might very well need Wheeler to fill the role of quasi-lefty specialist in 2011. It’s no secret that left-handed bullpen help is the Red Sox’ biggest weakness right now. Guys like Okajima, Andrew Miller, Rich Hill provide depth, albeit uncertainty for the Red Sox as far as left-handed relievers go.

The two left-handed pitchers in the Red Sox system of note are Drake Britton and Felix Doubront. There’s no chance we will see Britton in Boston this season, and the Red Sox project Doubront as a starter. I imagine that they’d prefer he spends his entire season as a starter, whether in the minors or majors, unless absolutely necessary.

Given the bulk of right-handed relief help that the Sox have (Pap, Bard, Jenks, Wheeler, Kyle Weiland and Alex Wilson in the minors), I wouldn’t be surprised to see the Sox make some sort of move to bring in left-handed relief help during the season if none of their options pan out. It’s unlikely they bring in someone with a high profile or pay anything expensive for him, but they could definitely bring in some more arms. Let’s just hope it doesn’t become a rotating door.

Dan is a Boston Red Sox and Boston Celtics featured columnist. Follow him on Twitter @danhartelBR.

Read more MLB news on