As opponents haplessly attempt to put wood on it, Deduno’s fastball also confuses the Pitchf/x computer system. Deduno’s movement – the diving, the darting, the running, et cetera -- tricks the system into believing he has multiple variations of a fastball. Plenty of those offerings are bucketed as cut fastballs. However, when asked about his fastball last year, catcher Joe Mauer confirmed that it is the same four-seam fastball with unpredictable movement.
The movement is not only unpredictable but it is extraordinary as well. The sink action on his fastball has been one of the best in the game. According to BaseballProspectus.com’s Pitchf/x leaderboard, Deduno’s sink on his fastball (2.88) is head and shoulders above (or is it below?) any other pitcher's dating back to the installation of the Pitchf/x cameras. In fact, the next closest in terms of movement is Cleveland’s sinkerballer Justin Masterson (4.36). Deduno’s fastball’s vertical movement more closely resembles a splitter than it does a standard fastball. Not surprisingly, because of the pitch’s action, Deduno has been able to get nearly 70% of all fastballs put into play to be beaten into the ground. The next closest pitcher in that category is St Louis’s Jaime Garcia (55%).
Of course, the downside to Deduno’s heat is that he exhibits little control over its final destination. He throws his fastball in the zone less than 50% of the time. Mauer said that his approach is to sit down the middle and let the natural movement take over. Watch the action of his fastball at the :23 second mark of this video: Mauer sets up down the middle and the ball runs across the zone and the left-handed hitting Alex Gordon is unable to make contact.
There are a lot of factors that contribute to the movement of this fastball. The whipping action at the release will make the ball dance. Another reason for the movement is his fastball grip. Consider what Stephen Strasburg demonstrates as his four-seam fastball grip:
Note the thumb positioning on the seam. Pitchers have variations on this placement, like putting their finger on the leather rather than the seam or curling their thumb in as well. Deduno takes the latter to the extreme. Take a look at the way he holds his fastball:
Deduno’s thumb is essentially at a right angle when he holds the ball. In the example above, the thumb is placed in a position to provide stability and improve command. Meanwhile, Deduno’s grip exchanges control for movement. Rather than the pad of the thumb making contact with the ball, the side of Deduno’s thumb is finessing the ball.
This is better highlighted in a comparison of rotation-mate Kevin Correia’s grip.
To be sure, Deduno’s grip is not exclusive to him. In just the Twins stable of pitchers alone, Jared Burton and Scott Diamond both have similar grips on their fastballs, both of who have had decent success with the pitch as well.
Deduno’s impressive if not erratic fastball has been one of his keys for success in 2013. While we may not understand how he flirts with disaster with his inability to target the strike zone consistently, we can see that what he hurls at home plate is very difficult to hit and the reason why he has a 3.32 ERA through seven starts.