What will the Nationals’ changes do to their offense?

We talked this morning about how almost all of the Nationals’ offseason moves have been made with the chief aim of improving their defense, and from a sabermetric standpoint, that looks to have worked. Taking the changes in the Nationals’ lineup for 2011, and assuming each player performs the way he did in 2010, the team should save about 18 runs next year.

But there’s a cost to all those moves, and it comes on offense. The Nationals subtracted their fourth and fifth hitter from last year’s lineup - Adam Dunn and Josh Willingham - and replaced those players with Jayson Werth and Adam LaRoche. And again, leaving everything else the same, those moves cancel out some of the defensive gains.

To evaluate the changes, we’ll use weighted runs created plus, a stat that measures all of a player’s offensive contributions on a scale, with 100 being average and higher scores equaling better outputs. The stat also accounts for changes in park factors.

Dunn had a 139 wRC+ last year, and Willingham, who only played 114 games, was just behind him with a 138, implying he would have had nearly the same contribution as Dunn had he stayed healthy. That’s a combined total of 277. Werth led all four players in our comparison with a 150 wRC+, but LaRoche was at just a 107. The two players total 257. And while LaRoche had put up better scores each of the last four years, Werth’s score was 15 points better than his previous high. He improved every year he was with the Phillies, and general manager Mike Rizzo said he thinks Werth can keep getting better, even though he’ll be 32 in May, but the Nationals will have to count both him and LaRoche surpassing what they did last year to make up for a dip on offense.

Mostly, if the Nationals want to improve, it will have to come from the same place it always needed to come from: everywhere but the middle of their order. The Nationals were abysmal at putting runners on base at the top of their order, and their lineup was thin after the No. 5 spot last year. They’ll have to hope Roger Bernadina and Michael Morse can handle the No. 6 spot together, and Danny Espinosa can bring some power to the lineup without posting strikeouts in bunches. The top priority, though, is at the top of the order. The team’s leadoff hitters were on base at just a .300 clip, and the No. 2 hitters, with a .326 OBP, weren’t much better.

And though it’s difficult to assume everything will go the same, the Nationals won’t be any better offensively if it does. They’ve traded some offense for some defense, and for the team to make a net improvement, the players they didn’t move will have to be better.