My batting reviews use types of batted balls to essay an assessment of how much a hitter's statistics might depart from their 'true talent level'. Another way to think about it is to see who might be hitting over their heads, getting that dying quail, or who might be suffering from an excess of 'at 'em' balls and may be likely to improve.
As anyone familiar with sabermetrics knows, one can evaluate batting events by means of linear weights. What this means is that a single is worth about two-fifths of a run while a home run, because it can drive in the men on base, is worth over three times a single. Research has revealed that types of batted balls can assign similar values. Line drives are worth a lot, while infield flies are almost as good as strike-outs. There is a problem in deciding what category to place a batted ball sometimes, especially the difference between a fly ball and a liner, as symbolised by the neologism 'fliner'. So one needs to treat these numbers with a degree of circumspection.
What this chart shows is the difference between a batted-ball linear weight and Fangraphs' wRC. wRC gives a supposed aggregate number of runs that should have been scored based on hitting events. Some people have flares falling in, while others hit the ball hard, but see it caught. The batted ball number also includes Ultimate Base Running, to make it more compatible with wRC. Note that the chart excludes pitchers' hitting. The first column is wRC, the second the batted ball expected runs.
Ian Desmond 79 61 +18 Bryce Harper 51 41 +10 Jayson Werth 100 94 + 6 Danny Espinosa 31 26 + 5 Adam LaRoche 84 80 + 4 Zach Walters 5 4 + 1 Michael Taylor 4 3 + 1 Tyler Moore 11 11 0 Nate Schierholtz 4 4 0 Ryan Zimmerman 32 33 - 1 Steven Souza 2 3 - 1 Anthony Rendon 100 102 - 2 Greg Dobbs 1 3 - 2 Jeff Kobernus 0 2 - 2 Scott Hairston 5 8 - 3 Sandy Leon 2 6 - 4 Wilson Ramos 38 43 - 5 Jose Lobaton 17 24 - 7 Nate McLouth 9 17 - 8 Asdrubal Cabrera 21 30 -11 Kevin Frandsen 19 32 -13 Denard Span 88 102 -14
I only did this analysis once for the Nationals in 2014 and, just like last time, Ian Desmond has been the luckiest batter, while poor Denard Span has been poorly rewarded for his efforts at the plate. Although I haven't don't a study of this, I use a rule of thumb that +/-5 is within reasonable expectations. So the main candidates to expect a decline from next year are Bryce Harper and possibly Jayson Werth (and Desmond), while we should expect more from Jose Lobaton, Nate McLouth, Asdrubal Cabrera and Kevin Frandsen (and Span). So it's just as well the Nationals picked up Span's 2015 option.