When Oscar Taveras was brought up after Matt Adams hit the disabled list, center field was neither necessary nor desirable for Taveras. Allen Craig could man first base, Taveras could play in right field while Jon Jay and Peter Bourjos could split center field. With the designated hitter available during that time, even more opportunities were available for playing time without pushing Taveras to center field. When Taveras returned to the majors, the situation had changed. Taveras has received three of his nine starts in center field due to Mike Matheny's desire to find playing time for Allen Craig as he works through his struggles. The Cardinals have several pitchers that suppress fly balls and we can expect Taveras' starts to come when those pitchers are on the mound.
Back in April, I wrote about Peter Bourjos and Jon Jay splitting time in center field. At the time, it appeared the two split their starts depending on the opposing pitcher as well as the Cardinals' starter. I used the chart below.
Much has changed since that time. The Cardinals have prioritized offense in the lineup which almost immediately diminished Bourjos' playing time. Joe Kelly left the rotation and has just returned while Michael Wacha has been replaced with Carlos Martinez. Bourjos has still recieved the occasional start, usually with fly ball pitcher Miller, but Jon Jay has taken over a majority of the starts with Taveras also sneaking in.
Changing the starters above and going a bit deeper than fly ball percentage can reveal which starter Taveras should be back in center field. Oscar Taveras in center field is not likely a long term solution for the Cardinals. He is just 22 years old and might get bigger as he ages. As he grows, he will eventually be pushed back to his natural position in right field. For now, he should be able to capably man center field occasionally while giving the offense the burst it needs (yes, the offense from Taveras is coming, be patient).
Here are the ground ball and fly ball rates of the current Cardinals' starters. (League average for fly balls is 34.2%)
The chart provides the reasoning for Bourjos making starts when Miller is on the mound and would seem to indicate any of the remaining pitchers would be acceptable for Taveras to make a start with Kelly and Martinez the most likely starters. Using fly ball percentage does slightly overstate how often the outfielder is needed as it includes home runs and infield fly balls while many batters will not put the ball in play at all. Changing the denominator can provide a little more perspective on how often each pitcher gives up a fly ball.
Instead of using fly ball percentage, I took a pitcher's fly balls, subtracted home runs and infield fly balls and divided by total batters faced to get a better sense of how often fly balls are hit to the outfield. While line drives are not included and they could be caught or make a difference when keeping a player to a single, because they become hits a vast majority of the time regardless of the defense, only fly balls were taken into account here.
For a frame of reference, the league average this season for the above statistic is 19.2%. Every pitcher but Miller is lower than the average when it comes to fly balls for their careers while Wainwright and Lynn have been slightly above average in addition to Miller so far this season. Wainwright's strikeouts have been down slightly this season. It clearly has not hurt either his ERA or his FIP, but it has caused an increase in the number of fly balls he has allowed. Fly balls are not necessarily a bad thing. Most become outs and in the Cardinals' home park, it is difficult to hit them out, but when trying to play to a team's strengths it is best to avoid Taveras in center if there are a lot fly balls likely to reach the outfield.
Oscar Taveras will not make many starts in center field, but they will need to be timed correctly. Based on the information above, Joe Kelly and Carlos Martinez are the ideal pitchers to limit any potential damage in the outfield so that the Cardinals can put forth the best hitting lineup possible (leaving aside the argument of whether Jay is a better hitter than Craig at the moment). It may be a good idea to continue to start Bourjos when Miller is on the mound. For the rest of the rotation, Jay has moved from number two defensive option to number one. Oscar Taveras is still the hitter the Cardinals need on a nightly basis to improve what was been a disappointing first half for the Cardinals offense.