Ryan Zimmerman, Defense, and First Base
Over the last couple of games Ryan Zimmerman's arm has become an issue, or put more aptly it has been made an issue by some. Before going very far in this I would like to introduce the Bill James defensive spectrum (read more about it here). The basic concept of it is that the most difficult positions defensively are in order catcher, short stop, second base, centerfield, third base, right field, left field, and first base. First base is the easiest position to fill defensively and not much defense is expected from that position. It is where an NL team might stick a player like Adam Dunn or Michael Morse to hide their defensive flaws. The limited defensive ability required to play the four bottom positions is why the saying exists, "Defense up the middle, power at the corners."
As far as Ryan Zimmerman goes he has consistently been one of the best defensive third basemen in baseball, but for a moment let's pretend his throwing is a real problem. Let us ignore the fact that both Ryan Zimmerman and Adrian Beltre have made around the same percentage of throwing to fielding errors in 2012 and both are considered two of the best defensive third baseman in baseball. Let us ignore that Zimmerman has only one year with a negative UZR and for his career has a UZR/150 of 9.8. Also forget all the great diving stops and bare handed pick-ups Zimmerman makes. Ignore the fact that many of his throwing errors come on balls no other third baseman gets to. Let's focus on the offense.
Ryan Zimmerman in 2012 has a wOBA of .343 which ranks him eighth among qualified third baseman. This has been a bit of a down year for Zimmerman as he has a career wOBA of .356. As a first baseman Zimmerman's .343 wOBA would rank tenth tied with Adam LaRoche and his career wOBA of .356 would rank seventh behind Corey Hart and ahead of Freddie Freeman. None of Corey Hart, Freddie Freeman, or Adam LaRoche is likely to ever get $100 million contracts in their careers. The reason that Zimmerman did is because he is a two way player. He plays above average offense at third and is one of the best defenders in the game. Moving him to first base may very well be one of the worst long term moves the Nationals could make.
Ryan Zimmerman is a 27 year old third baseman who is considered one of the best defenders at his position. This is not the type of player that moves across the diamond to first base. This isn't an almost out of baseball Troy Glaus just fighting for one more major league contract. Scott Rolen and Chipper Jones are both still playing third base at more of an advanced age than Zimmerman. The need to move Zimmerman to first is so small that it needs to stop being a thought.
And through all of this I have yet to mention Anthony Rendon. Most people's thoughts on Rendon are that he should either play third base or that the Nationals should trade either Desmond or Espinosa and stick him at second base. First thought is that it is much tougher for someone to move down the defensive spectrum than it is for them to move up it. Rendon doesn't even have that great of a reputation as a defender at third so the thought of moving him to second is borderline ludicrous. The obvious move is often the best move and with LaRoche having only an option for next season and Morse signed for that long the most obvious place for Rendon to play is first.
Zimmerman is the superior defender at third and first is considered the easiest defensive position to play and the type of position a hitter like Rendon should be playing. This is the obvious move and the one most likely to happen. Things can change between now and then, but taking a plus defender at third base and moving him to first because sometimes he makes a bad throw would go down as one of the worst baseball decisions in history.