The St. Louis Cardinals had a very successful 2013 season, winning 97 games en route to a World Series berth, but everyday center fielder Jon Jay did not have a very good year. Jay batted for a .276 average, posted a .351 on-base percentage, and slugged .370. Jay's .319 wOBA and 103 wRC+, were just a hair above average. Combined with a substandard season defensively, Jay posted 1.8 fWAR in 628 plate appearances over 157 games.
The Cardinals targeted center field as a position at which they could upgrade. In November, St. Louis traded their starting third baseman, David Freese, and reliever Fernando Salas (two arbitration-eligible players who had struggled in 2013 themselves) to the Los Angeles Angels of Anaheim in exchange for center fielder Peter Bourjos and outfield prospect Randal Grichuk. General manager John Mozeliak made no bones about the fact that he expected Bourjos, one of the game's top outfield defenders, to supplant Jay as the Cardinals' primary center fielder.
Early on, manager Mike Matheny appeared on board. Bourjos started on opening day and the season's second game. Jay started just two of the club's first ten games. As April progressed, Bourjos didn't hit and Jay did. At the conclusion of the season's opening month, Jay was batting .284/.351/.418 (.338 wOBA, 117 wRC+) and Bourjos .194/.252/.330 (261 wOBA, 64 wRC+). Center field became a time share with Jay eventually receiving the majority of the playing time. In the season's second half, Jay took 218 PA and Bourjos just 103.
Jay ended 2014 with .303/.372/.378 (.336 wOBA, 115 wRC+) in 468 PA. This line was far stronger than any projection system forecast. Even the VEB community, typically so optimistic, guessed low on Jay's 2014 offensive performance.
What was the key to Jay's resurgent 2014? Batting average, which is founded on Batting Average on Balls In Play or BABIP. While it wasn't particularly surprising that Jay's BABIP rebounded from 2013 to 2014—in fact, I wrote about Jay's batted-ball profile last year around this time—the extent of Jay's batted-ball success was a bit surprising. Jay's .363 BABIP was about as much above his career BABIP of .345 as his 2013 BABIP of .325 was below it. The following chart demonstrates how BABIP impacted Jay's fortunes as a batsman.
Jay's batting line undulates in correlation with his BABIP. This doesn't make Jay unique. Most batters are subject to the gods of baseball's BABIP whims. It's a highly volatile stat. What makes Jay somewhat unique is how dependent he is on an extremely high BABIP. Jay has established himself as a high-BABIP talent. His career BABIP through 2,424 PA is .344. In MLB history, just 39 players have notched 2,500 PA with a BABIP at least that high.
Because Jay hits for virtually no power (.075 Isolated Power in 2014 compared to MLB non-pitchers' .138 ISO) and low walk rate (6.0 BB% in 2014 compared to MLB non-pitchers' 7.8%), his offensive production is inextricably intertwine. Jay doesn't need to post a BABIP as high as the one he managed in 2014 in order to be a productive big-league hitter, but he does have to continue posting a BABIP that is a good deal higher than the MLB average, which is typically right around .300, in order to post a healthy batting line. 2013 is illustrative of this point. That year, Jay's batting line sagged quite a bit and his BABIP of .325 was still well above the MLB average BABIP.
If Jay is unable to hit for the type of average necessary to make him a productive big-leaguer, the Cardinals may find themselves revisiting the Bourjos-as-primary-center-fielder experiment from last April. The question is: How much would Jay's BABIP and BA have to fall in order for Matheny to go to Bourjos? If Allen Craig is in any way illustrative of how the manager might handle Jay, quite a bit.