To tackle the second question first, the reason we focus on BA is that the person or people who initially reported baseball statistics (I believe Albert Spalding in his Spalding Guide, but am unable to verify this after a Google search) decided it to be so. Walks were relatively less prevalent in the early days of major league baseball, thus it appeared that the batters who were best at getting hits were the most valuable. The rules of the game changed in the intervening century, but the habit of focusing on batting average did not.

But the first question remains unanswered - why is OBP better than batting average? Simply stated, because it is more complete. Bill James, in his New Historical Baseball Abstract, says:

"A good statistical analyst….asks three or four essential questions: 1. What is missing from this picture? 2. What is distorted here, and what is accurately portrayed? 3. How can we include what has been left out? 4. How can we correct what has been distorted?" (Pg. 339. Emphasis mine)

Clearly, batting average does not tell the whole story, because it excludes significant events like walks, sacrifices and hit batsmen. And all of these events have value, especially those that result in a batter reaching base (because a player can't score if he doesn't first reach base). Taken to its extreme, looking at batting average ignores over 200 plate appearances for Barry Bonds in 2003 (including 198 walks and 10 HBP) - about 1/3 of his times up. Does it make sense that a statistic that ignores 200 instances of a batter reaching base would be as valuable as a statistic that includes those events? I would say that it does not, and the way to include these events is to use OBP.

So, OBP is better than batting average, because it is a more complete statistic. Theo Epstein isn't the first person to recognize it. Oakland A's general manager Billy Beane places a heavy emphasis on OBP as well, as is documented in Michael Lewis' 2002 book Moneyball. Moneyball spends a great deal of time talking about Bill James' work, and credits him with influencing Beane. But James didn't create the statistic, either. According to Baseball-Almanac.com, Branch Rickey is generally considered to have been the first proponent of OBP when he was the Cardinals GM during the 1950's. So the stat has been around a long time, fifty years or more, but is just now getting the attention that it deserves.

And OBP deserves attention because it measures, in a way, how a team uses its outs. James was likely the first to note that outs are baseball's "currency". Because there is no clock, a team can keep hitting until it uses up its outs. And the flip side of OBP is, what percentage of a batter's plate appearances result in outs? A batter with a .350 OBP (good) makes outs 65% of his times up. A batter with a .400 OBP (very good) makes an out only 60% of his time up. Fewer outs means more base runners. More base runners means more runs. More runs equals more wins.

So let's get back to Mark Bellhorn. Why would Theo Epstein, the guy who was so hot to trade a guy who hit almost .300 the year before (Shea Hillenbrand), so willing to sign a career .230 hitter in Mark Bellhorn? On base percentage.

As of this writing, Shea Hillenbrand has a career .280 batting average, with a .317 OBP. Mark Bellhorn's BA is .231, but his OBP is .351. Let's compare a team of Bellhorns with a team of Hillenbrands, given one game's worth of outs to use.

Mark: 8.1 hits, 6.5 walks, 14.6 base runners. Shea: 10.5 hits, 1.8 walks, 12.3 base runners.

On average, the Bellhorns are going to get 2.3 more base runners (therefore 2.3 more chances to score) than the Hillenbrands every game. Certainly there is more work to be done, because hits move runners along faster than walks do, and there are 2.4 fewer hits for the Bellhorns. (Just as an aside, Bellhorn and Hillenbrand have almost identical Isolated Power numbers, that is, SLG - BA, or a measure of extra bases per at bat.) But base runner equals opportunity, and the Red Sox are not made up of nine Mark Bellhorns. The Red Sox lineup is loaded with sluggers who are just waiting to move runners around the bases. This is why Mark Bellhorn has value to the Boston Red Sox, despite his lowly batting average.

However, it remains to be seen how long Bellhorn will remain a major league regular. Simply stated, there just aren't any players like Bellhorn in the major leagues. By "like Bellhorn", I mean players who strike out a lot without any other highly desirable skill. As expected, the all-time strikeout list is filled with players with a lot of power. Those few who aren't power hitters were base stealers like Lou Brock or defensive whizzes like Devon White. Most also had respectable batting averages. Few and far between are guys like Bellhorn who offset high strikeout rates only with high walk rates. High strikeout/high walk batters are almost always power hitters (think Mike Schmidt and Jim Thome), even if they have low batting averages (Rob Deer is the poster boy here). When that secondary skill goes away (like Juan Samuel's base stealing ability), these players have a hard time keeping their jobs.

Bellhorn many be in the right organization if he hopes to get by on walks alone. The Red Sox also like his ability to get into deep counts, which can help get the opponents starting pitcher out of the game more quickly. More likely, Theo Epstein expects Bellhorn to regain the home run power he displayed when he hit 27 for the Cubs two years ago. There is a place in the major leagues for a high strikeout guy with some power and the ability to play several positions - Jose Hernandez comes to mind. Hernandez challenged the single season K record a couple of years ago while playing for the Brewers, but stayed in the lineup due to his 20+ home run power. (Ironically, Hernandez was traded by the Rockies to the Cubs for Bellhorn last summer.) Bellhorn has shown early signs of regaining his power stroke, with six home runs on the season thus far. Combined with the ability to play a couple of positions, see a lot of pitches and draw a lot of walks, Bellhorn can definitely be an asset to the Red Sox for the remainder of the season.

Statistics were gathered from ESPN.com and Baseball-Reference.com Baseball-Reference.com also has extensive listings of yearly leaderboards and career leaders in almost any statistical category, which helped in my research for this article.

Please also visit Roadduck99's baseball weblog, specializing in Portland Sea Dogs talk, at http://joesseablog.blogspot.com/ . You may also email him at Roadduck99@yahoo.com.