Michael Tonkin and the trade-off

About a week ago, Brandon Warne of Cold Omaha talked to Michael Tonkin about his fastball. In spite of many Twins fans arguing that Tonkin’s fastball was “straight,” it most certainly wasn’t for several reasons. First, because pitchF/X classified it as a two-seam fastball, a pitch that has more downward and horizontal tailing movement than the four-seam variety. Secondly, because pitchF/X last year said his fastball had almost identical movement to the average major league two-seam fastball.

However, pitchF/X can and does get its classifications wrong. Brandon discovered that with Tonkin, who stated that he hasn’t thrown a two-seam fastball regularly for a long time. Instead, it’s his arm angle (a low three-quarters) and spin rate (nearly 2,200 RPM) that cause the ball to tail more than most four-seamers, leading the pitchF/X algorithm to incorrectly identify the pitch as a two-seamer. You can get a great view of the movement here.

This strikeout pitch to Ortiz moved nine inches horizontally according to Brooks Baseball. Okay, admittedly I cherry-picked that pitch to help my narrative so here’s another. It may not look as impressive because it was thrown away to the righthanded Andrelton Simmons, but by again utilizing Brooks Baseball, we learn that it still tailed eight inches back towards the plate. That doesn’t scream “straight fastball” to me.

And yet in spite of a fastball with plenty of movement, Tonkin has been inducing fewer grounders than usual this year. It caught my eye when I saw his career-low groundball rate of 37.2% on FanGraphs recently. Admittedly that isn’t too far off from the 42.6% that he posted in 30 1/3 innings from 2013-2014, but it’s a severe drop-off from the 57.1% that he had last season over 23 1/3 innings. Thus far, it seemed like we might have been dealing with small sample sizes, so I looked at Tonkin’s minor league stats at the invaluable Minor League Central to see if his groundball rate in the high 30s was anything significant. I discovered that it was as his career minor league rate was 47.5% and although he did have a 34.3% rate over 39 innings at High-A Fort Myers in 2012, he spent the first part of his season at Single-A Beloit where his groundball rate was 50.5% over 39 innings. Other than his time at Fort Myers, he’s always induced grounders at a rate of 42.3% or better, so yes, that 37.2% number this year is a bit surprising.

Why is that the case then? Well, I went back to pitchF/X and found that Tonkin has lost quite a bit of movement from his fastball. Check out the change in vertical and horizontal movement throughout his career.

Or, if you’re more of a visual person, I have another GIF below. (The four-seam classification from 2013 is ironically correct, though that was due to pitchF/X labeling practically every fastball a four-seamer at the time.)

Yes, I understand that Tonkin has actually added vertical movement to his fastball but when your fastball was already getting less “rise” than most pitchers, adding to that is not a positive result in theory. However, where Tonkin has suffered by getting fewer ground balls, he’s made a significant gain elsewhere.

While two-seamers - or Tonkin’s four-seamer in the past - are great for getting grounders, they lack in their ability to get whiffs. Meanwhile, four-seam fastballs (and Tonkin’s 2016 fastball) are better geared towards getting hitters to swing and miss. Unfortunately, his increase in strikeouts have also come with an increase of home runs though, negating the positive changes he’s made this year. Otherwise, everything else about Tonkin’s game points to a perfectly adequate middle reliever with the stuff to make the jump to a setup reliever. I know quite a few Twinkie Towners and Twins fans in general disagree with me on that, but right now those home runs and a few too many hits are really all that are holding him back.

Since you’re probably wondering, I looked to see if there was a reason for Tonkin’s change in fastball movement when he said he hadn’t changed the type of fastball being thrown. I started by looking at his release and saw that each year he has moved a little more towards the first base side of the pitching rubber.

I’m not sure how exactly moving to one side of the rubber affects pitches other than the obvious change in angle towards home plate. Still, it looks like Tonkin has been tinkering to turn himself into a more effective reliever and though the results aren’t fully there, he has made some progress. It certainly appears that Tonkin has shown enough potential to be a part of future Twins bullpens.