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The Cardinals have made one major move this offseason, trading for Jason Heyward and Jordan Walden. Aside from bringing Walden into the bullpen, trading Shelby Miller presumably moved Carlos Martinez out of the bullpen and into the rotation. The Cardinals have made a few more under-the-radar signings affecting the bullpen, making the Cardinals relief corp considerably different than the one the Cardinals used in 2014.
The Cardinals bullpen was decidedly average last year. The rotation did its part for most of the season, preventing the bullpen from being too taxed. The Cardinals' 479 1/3 innings pitched ranked 18th out of 30 major league teams. Here are the rest of the Cardinals' ranks in 2014.
| Relievers | Cardinals | MLB Rank |
| K% | 21.3 | 19 |
| BB% | 8 | 9 |
| ERA | 3.62 | 17 |
| FIP | 3.61 | 19 |
| fWAR | 2.3 | 18 |
Closer Trevor Rosenthal was representative of the Cardinals mediocrity. Among the 25 pitchers with more than 20 saves in 2014, Rosenthal's 3.20 ERA ranked 19th, his 2.99 FIP was 13th, and his fWAR of 1.0 was 16th. Rosenthal's climbing walk rate last season is now well known. A rebound from Rosenthal in 2015 would go a long to improving the bullpen, but Rosenthal's 70 1/3 innings only accounted for around 15% of the bullpen innings in 2014.
The Cardinals divvied up most of their innings among eight relievers. Here are the stats for the Cardinals relievers with more than 30 innings last season.
| Name | IP | ERA | FIP | WAR | gmLI | K% | BB% |
| Pat Neshek | 67.1 | 1.87 | 2.37 | 1.8 | 1.57 | 26.7% | 3.5% |
| Trevor Rosenthal | 70.1 | 3.2 | 2.99 | 1 | 1.83 | 28.3% | 13.6% |
| Carlos Martinez | 57 | 3.79 | 2.94 | 0.8 | 1.57 | 21.0% | 8.4% |
| Seth Maness | 80.1 | 2.91 | 3.38 | 0.3 | 1.32 | 17.4% | 3.5% |
| Randy Choate | 36 | 4.5 | 3.58 | 0.1 | 1.06 | 21.6% | 8.8% |
| Sam Freeman | 38 | 2.61 | 3.79 | -0.1 | 1.06 | 20.7% | 11.2% |
| Nick Greenwood | 33 | 5.18 | 4.68 | -0.3 | 0.53 | 11.9% | 3.7% |
| Kevin Siegrist | 30.1 | 6.82 | 4.62 | -0.3 | 1.47 | 26.4% | 11.4% |
The gmLI (from Fangraphs) column shows the average leverage index when a reliever entered the game. Generally, the higher the legverage index, the better reliever a team would want in the game. The Cardinals did a relatively good job with usage in 2014. Rosenthal, Neshek, and Martinez were the three best pitchers and they had the three highest gmLI. Kevin Siegrist was expected to take on a high leverage role for the Cardinals, but it became clear that he was not as effective as had been in 2013.
Ideally, Randy Choate would have a higher gmLI. He should be entering games to get one guy out, although he was not used that way last year. Sam Freeman and Nick Greenwood look to be on the outside heading into Spring Training. With the additions of Jordan Walden, Matt Belisle, newly signed Carlos Villanueva, and newly leveraged Marco Gonzales, the Cardinals bullpen should have a different look in 2015.
Trevor Rosenthal, Seth Maness, and Randy Choate will likely have similar roles, but the newcomers should have a big impact. Here are the projected numbers for the Cardinals bullpen from ZiPS, available at Fangraphs.
| IP | FIP | ERA | |
| Trevor Rosenthal | 77.7 | 2.62 | 2.55 |
| Jordan Walden | 49.7 | 3.00 | 3.08 |
| Matt Belisle | 65.7 | 3.22 | 3.43 |
| Marco Gonzales | 108.3 | 3.84 | 3.74 |
| Seth Maness | 78.3 | 3.39 | 3.56 |
| Carlos Villanueva | 96.3 | 3.60 | 3.92 |
| Randy Choate | 30 | 3.46 | 3.60 |
| Kevin Siegrist | 52 | 3.43 | 3.29 |
With Neshek and Martinez gone from the bullpen, two of the better relievers from last season are gone, but an improvement from Rosenthal and solid seasons from Walden and Belisle should make up for the losses of those pitchers. A similar season from Maness can be expected. Both Gonzales' and Villanueva's numbers include starter innings. As relievers only, their numbers should be better than those listed above. As a reliever last season, Villanueva pitched 58 innings with a 2.64 ERA and a 2.99 FIP.
Bullpen performance varies greatly from year to year. The Cardinals saw both the good and bad of that last season in the performances of Pat Neshek and Trevor Rosenthal, respectively. Relievers get injured and disappoint, and sometimes a player's statistics are simply negatively impacted by pitching so few innings every year. Despite those caveats, the Cardinals bullpen has the potential to be significantly improved from last season.