Recently, it was reported that the Colorado Rockies were considering signing free agent Daniel Murphy to play first base. Murphy, who has been the Mets' primary second baseman over the last few years, had his fair share of struggles on defense, highlighted by his costly errors in Games 4 and 5 of the World Series. My first reaction to seeing this rumor was one of skepticism. Why would a team move a slightly above average hitter from a position where offensive production is often seen as a bonus to a position where offensive production is required?
Murphy has consistently been an above average hitter throughout his career. He has a career wRC+ of 109, and since his breakout 2011 season (.320/.362/.448, 126 wRC+), he has put up remarkably consistent numbers over the last four years.
Murphy is a high contact hitter who gets on base enough and hits for enough power to be slightly above average overall. Putting the layoff streak aside, nothing in his offensive profile stands out as unusual. Murphy is well above average among second basemen, though, who in 2015 combined to hit for a .261/.315/.391 batting line with a 93 wRC+. His 110 wRC+ ranked eighth among qualified second basemen in 2015.
If Murphy were shifted to first base, however, he would immediately become below average offensively for his position. The league average batting line for first basemen in 2015 was .259/.336/.444 with a 113 wRC+. With that being said, Murphy would still be a major improvement for the Rockies, who effectively had a black hole at first base in 2015. The Rockies' primary first basemen were Ben Paulson, Justin Morneau, and Wilin Rosario; combined, the trio hit .275/.317/.431 with an 86 wRC+ and -0.2 fWAR. While this slash line may not seem different from Murphy's 2015 slash line, it is important to keep in mind that the Rockies play half their games at Coors Field. The 86 wRC+ is a more accurate representation of their offensive performance, since wRC+ is a park-adjusted statistic. If Murphy would have played his home games at Coors Field, he likely would have had a much better slash line, but his wRC+ would have stayed the same.
So what about Murphy's defense? If he were shifted to another position, he would be less likely to cost his team runs defensively at second base. However, we must take into account positional adjustments, since second base is a more demanding position defensively than first base. According to the positional adjustments available on FanGraphs, the difference between an average second baseman and an average first baseman is about 15 runs per season. For Murphy to be worth the same amount of value defensively, he would need to be approximately 15 runs better defensively at first base than he was at second base.
As it turns out, Murphy has played some first base in his major league career. Most of his playing time at first base came in 2009 and 2011, but he still has a sizable sample of 1525 innings at the position. In his career at first base, Murphy has posted a UZR/150 of 5.8 with 20 defensive runs saved. In his career at second base, Murphy has a UZR/150 of -6.3 with -42 defensive runs saved in 4343 total innings. Using UZR/150, we would expect Murphy to be approximately 12 runs better at first base than at second base over the course of a season, excluding the positional adjustment. By defensive runs saved, this difference is even more drastic at nearly 30 runs per season.
If we say that the actual difference is somewhere between these two numbers, then it seems quite possible that Murphy could more than make up for the positional adjustment and provide greater defensive value as a first baseman than as a second baseman. In a weird way, Murphy could be one of the few (if not the only) "defense-first" first basemen while providing solid but unspectacular offense. Given the lack of first base options on the free agent market, signing Murphy and moving him to first base may not be such a bad idea after all.