St. Louis Cardinals: A Look at Trevor Rosenthal’s Fastball Location

Trevor Rosenthal has gradually moved his fastball location down in the zone over the past few years. That’s a bad thing for the St. Louis Cardinals.

Prior to hitting the Disabled List on July 26^th, Trevor Rosenthal struggled mightily for the St. Louis Cardinals. He had already lost the closing job in June to Seung Hwan Oh. His 5.13 ERA and 4.14 FIP were on pace to be the highest of his career. Batters .442 BABIP and his 16.2% BB% were also on pace to be career worsts.

Rosenthal came back to action on September 16^th and was much more successful. Based on results, he appeared to look like his dominant self. He cut his walk rate to 6.7%, his ERA to 1.29, and his FIP to 1.72. His BABIP against decreased to more respectable .350 (granted, the sample size here is only 7 innings and 30 batters faced).

This apparent success prompted Viva el Birdos to suggest that Trevor Rosenthal had returned to form. They proposed that refined fastball location contributed to Rosenthal’s post-injury success, citing this fastball heat map:

Rosenthal was now more precisely locating his fastball in an area he had been targeting throughout the season. This would bode well for decreasing Rosenthal’s walk rate, which would help his overall performance.

I decided to look through Rosenthal’s FanGraph’s page. The first thing that jumped out to me is that hitters BABIP against Rosenthal’s fastball has risen every single year since 2013. With BABIP, batters AVG, OBP, SLG, and OPS against the fastball have all also increased each year. For a pitcher who throws more than 80% fastballs, that is a really bad sign.

Trevor Rosenthal will hurt the St. Louis Cardinals if he fails to locate his fastball higher in the zone.

While Rosenthal’s location may have been more precise following his return from injury in September, the location he hit during this period is worrisome for the St. Louis Cardinals. With Rosenthal’s velocity, his fastball is most effective when located at the top of the strike zone or slightly above. Fastballs in the lower two-thirds of the zone are easier for hitters to handle.

In fact, after returning from injury, hitters actually squared him up better than they ever had. While his 1.29 ERA looked great, Rosenthal gave up lines drives at an extremely high 47.4% rate. This suggests that there was quite a bit of good luck on Rosenthal’s side in September and October, and that his fastball problem was not solved by his more precise location down in the zone.

This trend is nothing new. Over the past few years, the declining success of Rosenthal’s fastball is most likely due to an increasing tendency for him to locate it lower in the zone. The following are Rosenthal’s fastball location heat maps over the past four seasons:

Clearly, Rosenthal’s focus locations (the darkest areas) with the fastball have been gradually moving down in the zone, especially since 2014. The result has been an increase in LD% and GB%, which would support a rising BABIP. Inducing fly balls is important for power pitchers, as the result is often an easy out when the hitter doesn’t catch up the high heat. Rosenthal’s FB% was down to 14.3% last year from 31.7% in 2013.

Since it appears that Rosenthal is making a concerted effort to work lower in the zone, I expected to find that, for some reason, he must be more effective when he locates his heater in the bottom two-thirds of the zone. Of course, the reality is that exact opposite.

Below, I examined how hitter’s fared against fastballs between 95 and 100 MPH in the top third, middle third, and bottom third of the strike zone. I divided this analysis into two periods, the first from 2013 to 2015 when Rosenthal had his most success, and the other in 2016. The number of pitchers in each group varied slightly due to minimum sample size requirements.

The results are about what we would expect. On average, batters hit worse against high velocity fastballs when they are located in the top third of the zone. This pattern held for Rosenthal when he was at his best and continued to hold true in 2016.

It’s really no wonder why Rosenthal’s fastball has had declining success over the last four years. Hitters are best against his fastball when he puts it in the lower two-thirds of the zone. Yet,  Rosenthal has continued to locate his heater lower in the zone at a higher rate each year.

Next: Making New Years Resolutions for the Cardinals

Fastball control has always been an issue for the St. Louis Cardinals former closer. If Rosenthal really has figured out his fastball command now that he appears to be healthy, he needs to focus on elevating his fastball. Failing to work the pitch higher in the zone will result in another rough season in 2017 for Trevor Rosenthal.