Here's why knuckleball pitchers throw terrible fastballs

I wrote earlier this week about Dan Johnson, the former Blaine HS standout who spent 10 years in the majors as a first baseman/DH — the last with St. Louis last season — but is now trying to re-imagine his career at age 37 as a knuckleball pitcher. He’s plying his new trade with the local St. Paul Saints, to strong results. In his past three American Association starts, he’s allowed a total of one run in 18 2/3 innings.

And Saints manager George Tsamis, who said he has never liked knuckleballs, said Johnson is changing his opinion — in part because Saints opponents are telling the team the pitch is “unhittable.” Multiple MLB organizations are tracking Johnson’s progress, so there is a real chance he could make it back to the majors — perhaps as a versatile, 2-for-1 type player who could be a spot starter both in the field and on the mound.

As someone who dabbled with the knuckleball, too — I believe the last one I threw in an actual game was an 0-2 knuckler in American Legion ball that didn’t knuckle, was knocked to right for a base hit, and prompted my manager to storm out of the dugout and order me to never throw the pitch again — I enjoyed talking shop with Johnson about the peculiar but effective pitch.

He showed me his grip (two fingers, no seams). Johnson told me how he has messed around with the pitch since youth baseball, when his dad dubbed it the “dancing dazzler.” But most interestingly, Johnson explained why he doesn’t have much fastball to go with the knuckleball, a common refrain among knuckleball pitchers in history.

Johnson said he tops out at around 84 mph, which is common. I always assumed it was because knuckleball pitchers developed the pitch because they lacked velocity. Perhaps that’s part of it, but Johnson also explained a different reason:

“It’s hard to throw a fastball in the knuckleball arm slot, and you have to throw it the same,” he said. “Otherwise the batter knows which is the fastball and which is the knuckleball.”

That makes a ton of sense, and it was something I certainly never paid attention to when I was pitching. Say Johnson could throw more like 86-88 if he put more behind a fastball and threw it from a different arm slot. A good hitter would spot the change in mechanics and delivery and be quite likely to hammer the pitch. At a slower speed but with the same delivery and slot, at least a fastball has the element of surprise when a pitcher is throwing 85-90 percent knuckleballs, as Johnson says he is throwing these days.

Numbers on Steven Wright of the Red Sox seem to support this theory. This piece suggests Wright could throw 90 mph back in 2011, when Cleveland approached him about throwing his knuckler full-time. But his average fastball these days clocks in at around 83-84 mph, per Fangraphs. The switch proved to be a great thing for Wright’s career, by the way. He’s 13-5 for the Red Sox this season.

Johnson’s a long way off from doing that. But slow and steady with the knuckleball — and the fastball — can still win a race.