Whenever I look at anyone’s numbers and try to find out what’s wrong, it has a courtroom-like feel for me.
I decided to take an even closer look at Rondon by looking at his advanced stats such as pitch type, velocity, pitch values, etc.
As I mentioned before, Rondon completely threw out his cutter after the 2015 season. He has also severely decreased his amount of two-seam fastballs from 29.2% of the time in 2015 to just 3.7% today.
As a result of those two decisions, Rondon has distributed a total of 31.6% of his former arsenal into two main pitches: his four-seam fastball and his slider.
First, let’s call his four-seam fastball to the stand. He currently uses it 58.3% of the time, by far the most of any of his pitches. Surprisingly, Rondon’s numbers with the four-seam fastball have remained pretty consistent throughout his career. Four-seam fastball verdict: Not Guilty.
Next, I call Rondon’s slider to the stand. Rondon currently uses his slider 35.8% of the time, his career high. All of the advanced stats on Rondon’s slider are down dramatically since 2015.
For example, according to Fangraphs, Rondon’s wSL (slider runs above average) fell from 7.1 in 2015 to -0.8 this year. Talk about a dramatic difference. The verdict on the slider: Guilty.