As the Nationals ramp up their negotiations to land a center fielder, consider at least one reason Denard Span is so valuable to the Nationals, a team that since the very first days of their time in Washington – back to when Jim Bowden was excoriating Endy Chavez for his impatience at the plate in the spring training 2005 – has not been able to land a certified center fielder:

Over last season and this season, Nationals leadoff hitters have combined for a .286 on-base percentage, which ranks last among major league teams, 20 points below the 29th-ranked Baltimore Orioles.

Span, who is recovering from a concussion, has a career .366 on-base percentage, and he is regarded as an excellent defensive player. He fits precisely what the Nationals need. And, as a very important bonus, Span is under team control through 2015. He is long-term solution to what has been a long-term problem.

Neither of the other two center fielders the Nationals have discussed, B.J. Upton and Michael Bourn, fit quite as perfectly. Bourn, whose range in center is nearly unparalleled, has a career .338 on-base percentage. Upton strikes out a ton and, while he has a career .340 OBP, it’s just .318 since the beginning of the 2009 season. Upton has value, but not in the areas the Nationals are most lacking.

Another crucial point is that both are controllable through 2012 only, so either becoming a long-term fit would require giving up players now and an immediate financial committment.

Span may not be the kind of player who makes the Nationals an instant contender, but he fits their needs perfectly and could play a vital role in making them a factor. That’s the Nationals could trade reliever Drew Storen for him. No one in the organization wants to deal Storen. But you have to give up to get, and trading a reliever – even one like Storen, who is good now and under team control through 2016 – for an everyday leadoff hitter and center fielder is something worth doing.