For much of this season, first base has been a weak spot for the Cardinals. Early in the season, the combination of Matt Adams and Mark Reynolds failed to provide adequate offensive production at the position, which is typically reserved for good offensive players. This situation became much worse when Matt Adams tore his quad and went on the DL, leaving Reynolds as the primary first baseman, supported by backups Xavier Scruggs and Dan Johnson.
The Cardinals' first base situation was supposed to be resolved in late July when the team gave up prized pitching prospect Rob Kaminsky to acquire Brandon Moss. I, like many other Cardinals fans, was not a big fan of the move, as the trade seemed like a rare instance of John Mozeliak panicking, in large part due to the expected loss of offense resulting from Matt Holliday reinjuring his quad.
Since joining the Cardinals, Brandon Moss has done little (outside of an impressive seven-game stretch) to show definitively that he is the Cardinals' best option at first base. In fact, Mike Matheny appears to have used a "hot hand" approach regarding playing time at first base. Since the start of August, Brandon Moss has started 21 games at first base, compared to 19 starts for Mark Reynolds, six for Stephen Piscotty, three for Matt Adams, and one for Matt Carpenter. (Moss and Reynolds also made a handful of starts at left field and third base, respectively.)
Going back to the idea of the "hot hand," it is clear that Matheny's preference has to give playing time to the player that he thinks is performing the best at that particular time. At the start of August, Brandon Moss started five of six games at first base. Then, Mark Reynolds started thirteen of the next eighteen games. Then, Matheny went back to Moss, who started in eleven of the next fourteen games.
Over the last thirteen games, though, things have gotten more complicated. Matt Adams has returned from the DL and started three games at first base. Reynolds and Moss have each gotten two starts. Most notably, Stephen Piscotty has started six times at first base, likely due to the returns of Matt Holliday and Randal Grichuk and the emergence of Tommy Pham.
While first base may not be Piscotty's natural position, he has received playing time there due to his superior offensive ability. This season, Piscotty has posted an impressive .313/.369/.500 batting line with a 137 wRC+ in 236 plate appearances. None of the other first base contenders (Moss, Reynolds, Adams) have hit anywhere close to that level in 2015. Mark Reynolds is closest with a 99 wRC+ in 414 plate appearances, and he has effectively been replacement level this season (0.1 fWAR to be exact).
Given the differences in offensive performance between Piscotty and the other first base candidates, it may seem like a pretty easy decision to play Piscotty at first base on a regular basis. Indeed, Benjamin Hochman of the Post-Dispatch recently made the case that Piscotty should be starting at first base in the playoffs. At this point, I don't necessarily disagree with this statement, but I do think the first base decision is not quite as clear cut as it may seem to be.
The biggest concern I have for Piscotty is that he will not be able to sustain his .386 BABIP. Besides the fact that it is nearly impossible for any hitter to sustain a BABIP this high, Piscotty has not done anything in his minor league career to make us think he can consistently run ridiculously high BABIPs. At every level of the minor leagues in which Piscotty has totaled more than 100 plate appearances, he has posted BABIPs between .300 and .320. Piscotty also doesn't have the above average speed needed to boost his BABIP via infield hits.
In general, Piscotty's rest of season projections are quite pessimistic, with ZiPS' projected wRC+ of 102 being the most optimistic. In fact, Piscotty's rest of season ZiPS projected wRC+ is third among the Cardinals' first basemen, behind Brandon Moss (117) and Matt Adams (105). Mark Reynolds is in fourth, with a 98 wRC+ projection.
If we trust the projections, then it seems clear the Cardinals' first base situation is far from settled, and I haven't even taken defensive ability into consideration. Piscotty has played all of 51 innings at first base so far, which means that his fielding metrics (which say he's been pretty average so far) have very little meaning. If we assume that Piscotty is at least a step below the Cardinals' other first basemen defensively due to his inexperience, then it may be very hard to justify playing him at first base going forward, especially given his inevitable offensive regression.
This may seem like a crazy thing to say, given how well Piscotty has played so far, but this particular situation does a great job of illustrating the difference between what a player has done and what a player can be expected to do going forward. Given the way Mike Matheny has managed the first base situation this season, it is likely that he will continue playing Piscotty until he 'goes cold," so to speak. If and when this happens, it is possible that Matheny will feel the need to give more playing time to someone else at first base.
If this situation occurs, then I think Brandon Moss should be the first option that Matheny should turn to, assuming he is completely healthy at this point (which is a legitimate question given his offseason hip surgery). Moss has the best projection of the Cardinals' first base options, and he's shown flashes of greatness in his time with the Cardinals. It should also be noted that the Cardinals' front office presumably had good reasons for acquiring Moss, especially considering the price they paid to acquire him. If they truly thought highly of Moss, it would be silly for them to bail on him after just 132 plate appearances.
The Cardinals have struggled all season to find consistent production at first base. At the moment, Stephen Piscotty appears to be the Cardinals' preferred choice at the position, but he might not be the best option going forward. With the playoffs approaching, the Cardinals are running out of time to figure out who their best option at first base really is.