Most Nats fans have come around on the point that Denard Span is an upgrade over Michael Morse. You replace a negative 20 runs in UZR/150 with a positive 4.6 and you upgrade the Nats weakest line-up spot from the past few season with a career .357 OBP hitter. Defense is one thing but Morse was a left fielder/first baseman and both of those positions are known for offense. At the end of the day people are going to see the Nats replacing a career .839 OPS and .363 wOBA hitter with a .746 OPS and .332 wOBA one. That ignores a large chunk of offense and most of Denard Span's added value outside of defense and OBP, and that is base running.
Think about it for a second. What is the first stat you look at when judging a player? Is it their slash line, wOBA, WAR, what? How often is the first stat checked a base running or defensive stat. WAR does try to account for those things and it does a good job of it, but do most realize it or do they even care or are they even the ones I am writing this for? I often even forget that the base running aspect of fWAR can be viewed on Fangraphs. BSR/UBR is the stat and it takes everything into account. It even counts for when a batter doesn't run on a strong armed outfielder. Take a look at the primer. Morse is a -10 BSR/150 base runner and Span a 6.3. As with defense, that is a large increase in value. From base running and defense alone Span is worth four wins more than Morse.
This is all a little complex and may be hard for some fans to get a grasp of. Stats should be simple so that everyone can understand them. Converting base running to a runs number like UZR is nice for those of us that cotton to that sort of thing, but what about for the fans that don't. Think about how easy wOBA is to explain. It is a formula that values the type of hit and the times on base to a weight and is then converted to be read like OBP. wOBA also tries to factor in base running, but only with steals and caught stealing and in my estimation does a poor job of it. All the ways of reaching base are given context weights of base outs situations while a stolen base is weighed as 0.25 runs and a caught stealing 0.50 runs. Meaning that Ian Desmond who stole 21 bases and was caught only 6 times for a 78% success rate is gifted with 2.25 runs in the wOBA formula where a single homerun counts as 2.058 runs. One single homerun is not almost as valuable as 21 stolen bases, in my opinion. And that is what we're trying to measure when comparing Span to Morse. Span is a speed player and Morse a power player. There are no good stats that accurately measure power and speed and give us a way to compare them.
Making a simple stat that measures both power and speed isn't all that difficult. I am sure you know what SLG is. It is the main stat by which power is judged and it is one of the simplest formulas in baseball. It is total bases divided by at bats. Simple see. ‘Total bases’ is a stat that measures bases that a batter batted themselves to. It isn't too difficult to go on ahead and add bases ran to into the total base stat and come up with an offensive stat that measures both power and speed equally. For Morse we will only look at his career with the Nationals as his power took a huge uptick, and for Span we will look at his entire career. Also not all bases ran to will be counted. Going from first to second on a single isn't a product of speed or any good base running. It is just playing baseball; the same with going first to third on a double or first to home on a triple.
When adding in stolen bases, bases taken (bases advanced on a passed ball, wild pitch, sac fly, ect) , extra bases taken (advancing more than one base on a single and more than two on a double) and subtracting caught stealing and times picked off to career total bases Span's SLG upgrades to .503 and Morse's .561. Morse's power still gives him a sizable advantage but it is much closer than their unconverted SLG of .389 for Span to .514 for Morse. Now we can go ahead and add OBP to this to make an OPS type stat that is .860 for Span and .904 for Morse in his time with the Nats. It is closer than it was before and Morse still has the advantage, but Span is not nearly the offensive downgrade his standard slash line would lead one to believe.
Simply adding more bases to total bases may not be the overall best way to compare power to speed, but it is a way. It gives us even more of an idea of what Span is going to add to the team offensively and that the Nats aren't sacrificing much if any offense for defense. Consider for a second that the Nats lead-off hitters in 2012 had 762 plate appearances and reached base safely 32.5% of the time. Figuring that Span will do so at his career average of 35.7% and will get around 650 of those plate appearances he will reach base 232 times. If the Nats get an equal number of PA from the lead-off spot in 2013 as 2012 and other Nats hitters perform to last season's average then the Nats are looking to go from 247 base runners from the lead-off position to 268. Those 20 extra bases might not sound like a lot, but they are 20 less outs and 20 more opportunities for either Werth or Harper to bat. And if we count a base as a quarter of a run it is five extra runs or half a win.
Add that all in to everything else we have said Span is doing for the Nationals and he could be as much as a five win upgrade over Morse due to defense, base running, and OBP from the lead-off spot. That is a large leap for a team that won 98 games in 2012. Make of that what you will. It is going to be interesting to see how all this plays out in reality and if Span's base running really does help to close the offensive gap between he and Morse.