The Cardinals made a decision that they had to make with Trevor Rosenthal. The only question is: what took them so long?
Trevor Rosenthal has been a key part of the Cardinals bullpen for the past three years. During that time, he struck batters out at alarming rates and rarely gave up home runs. However, the Cardinals should have been prepared for what has happened this season.
I’m not saying that they should have known it was coming, but they should have known it was a possibility. In 2014, Rosenthal saved 45 games while walking more than five batters per nine innings. Even though he closed a lot of games, the Cardinals should have been worried about him.
That high a walk rate makes success incredibly difficult to sustain. Even though he got his walk rate down to 3.3 batters per nine innings last season, the Cardinals should have been concerned about his control the whole time.
The Cardinals are one of the best teams at applying advanced analytics. In this case, they completely mishandled it. They ignored his walk rate and drooled over his strikeout totals. The strikeouts have remained, but the control has gone too far downhill.
When looking at Rosenthal’s numbers, it’s pretty clear that walks would be the reason why he would eventually stop being effective. That is exactly what has happened this season. Rosenthal is up to an ugly 7.9 walks per nine innings. He has also given more home runs too but that is due to a ridiculously high home run per fly ball rate.
The problem is definitely control, which is not a surprise. Rosenthal seems to have forgotten where the plate is, and the Cardinals took three months to act on it. The team would have made this decision much sooner if they were ready for the situation they are currently in. It appears that either Seung-hwan Oh or Kevin Siegrist will now take over as closer. Either one is a fine choice, but the Cardinals are making that choice about a month later than the optimal time.
Some of his bad pitching is just due to opponents having a higher BABIP than usual against him, but that does not change the walks. Check out the differences in location on these heat maps from baseball savant. The left map is 2016 only and the right one is his entire career.
Those maps are for his fastball. There is no big change here except for the fact that he is trying to catch the inside corner on righties more often. Whether or not it’s working is difficult to tell, but the big differences come in his off-speed stuff.
Here is his changeup, and you can see the problem. Even though the location is not that far off, it’s literally the difference between a strike and a ball. Last year, those pitches were coming in at the knees. Now, batters are taking those pitches for balls. His changeups are also much closer to the center of the plate, so it’s easier for batters to get a good look at them or make contact if they must swing.
These heat maps are from his slider. I have no idea what the problem is, but he is not getting this pitch down at all. When your slider is reaching the top of the zone more often than it reaches the bottom, you have a big problem.
These last ones are for his curveball. Rosenthal rarely throws this pitch anymore, but it may demonstrate the problem the best. He is trying to throw the curve down-and-in to right-handed batters. Instead, his curve is going up-and-away. If he is that far off in control, then it’s no wonder that he is walking so many batters.
Given that Rosenthal never displayed good control, the team should have been prepared for a season like this. He throws his fastball 80% of the time and that pitch has been fine. The problem is that 20% of the time when he goes away from his heater. The curveball is really the only pitch that shows a huge difference in location, but his other pitches have been off just enough.
A team as analytically sound as the Cardinals should have recognized that his walk rate may spike at any time. The team really should have been ready for this outcome. For most pitchers, a change in location on twenty percent of your pitches would not mean walking four extra batters per nine innings.
The Cardinals are making the right decision now, even if it is later than it should have been. They also should not just keep Rosenthal as a setup man. He needs to be in low leverage situations, and middle relief looks like the best destination for him. A minors stint would not even be the worst thing in the world. Either way, the Cardinals are finally taking the ball from Rosenthal’s hands late in the game, and that is for the better.
Photo Credit: Jeff Curry – USA TODAY Sports