What does Pitchf/x reveal about new St. Louis Cardinals reliever Jordan Walden?

The "other guy" received in the Shelby Miller and Tyrell Jenkins for Jason Heyward mega-deal is Jordan Walden, a right-handed relief pitcher with a hop in his mechanics that rivals the hop seen on his fourseam fastball. As Ben discussed in his post-trade roster matrix and payroll post, MLB Trade Rumors projects Walden's 2015 salary to be $3 million, which is reasonable given his potential and the fact that he is entering his second year of arbitration. If he is able to stay healthy, Walden and his blazing fastball will be inserted into a late-inning, high-leverage relief role—something similar to that of Pat Neshek this past season, which, for better or for worse, was essentially the "eighth-inning bridge" to Trevor Rosenthal.

Career (unless otherwise noted) PITCHF/x data via BrooksBaseball

Walden has effectively been a two-pitch (fastball, slider) power reliever over the course of his five-year MLB career, but in this past season with the Braves, he began throwing more changeups (2014: 10.65% versus career: 6.34%), and though the sample size of results is small (16 at bats ending on the pitch), it seems to have been an effective weapon for him (.188 BAA, .250 SLG, .063 ISO, with 11 strikeouts). Even more notable is that the whiff rate on Walden's changeup was 29.35% in 2014—three times higher than his fourseam fastball (10.85%) and ~1.5 times higher than his slider (20.47%). If having one pitch with a whiff rate over 20% is like owning a handgun, having two pitches over 20% might as well be considered wielding a grenade launcher.

For what it's worth, Walden's changeup and slider whiff rates rival those of Aroldis Chapman in 2014. Remember that post I wrote on the beautiful changeups of Rosenthal and Michael Wacha? As you may recall, I raved about how Rosenthal induced whiffs 44.55% of the time hitters swung at his changeup. Well, Walden's "whiff per swing" percentages were 60.00% (!) on his changeup and 54.32% on his slider in 2014.

Next on the PITCHF/x agenda is the velocity of Walden's fourseam fastball. His career average stands at 97.54 MPH (for perspective, Rosenthal's is 98.08 MPH), which is necessary given the fact that he has thrown it three out of every four pitches at this stage in his career. Our friend, Daren Willman, from Baseball Savant, provided an interesting tidbit on Walden's fastball:

Only one player besides Aroldis Chapman has thrown 100% of their fastballs for a season 95MPH+. Jordan Walden in 2010 http://t.co/piwiOEE0Pp

— Daren Willman (@darenw) November 17, 2014

I am not really sure how relevant this is given that it was roughly four years ago, but it is interesting to note nonetheless. However, another more concerning thing to note is that Walden's fastball started out averaging 99.60 MPH during his rookie season (2010), dropped to its lowest average velocity of 96.66 MPH in 2013, but has since seen a very slight uptick to 96.95 MPH last season. If his fastball velocity is able to hold steady in the 96 to 98 MPH range, he will continue to be successful, but if it continues the downward trend we saw prior to last season, how successful can he be? We will soon find out.

The last thing I would like to note regarding Walden's PITCHF/x data is his dragless horizontal movement. In 2014, from the batter's perspective, his slider (positive 5.83 inches) and changeup (negative 12.09 inches) had a difference in average horizontal movements of nearly 18 inches. I know I've brought up the set-up pitch on numerous occasions already, but the disparity between these two pitches is almost unfair on opposing hitters and is likely a huge factor in Walden's high whiff rates. The velocity, combined with a considerable amount of movement and a unique pitching motion, makes Walden an effective high-leverage reliever.

Lower-body mechanics (as I will dub the "J-Wald Hop")

I am not going to discuss Walden's upper-body mechanics as I am sure it will be addressed in the comments section shortly. However, I will talk about his lower-body mechanics—specifically his hop (see the above screenshot) as he drives off the pitcher’s rubber. I remember watching him, and quite honestly, being irritated by him, in the 2011 All-Star Game because I had convinced myself that he was balking on every single pitch. After reading through the applicable portion of the MLB rule book, it does not appear that what Walden is doing should be classified as a balk, which is refreshing considering he is now a member of the Cardinals.

Injury history

Per his Baseball Prospectus player card, Walden has missed 108 games due to injury since the start of the 2012 season, and seemingly all parts of his body (thigh, hand, groin, lower back, forearm, elbow, and shoulder) have been affected. Of those 108 games missed, 32 of them occurred last season due to a left thigh strain. It was reported that this trade was completed without physicals being performed, and though Walden is obviously not the headliner in a trade involving Heyward, this is still notable. As previously stated, MLB-TR projects Walden to get $3 million in 2014. If I'm Mozeliak, I first discuss with Walden's agent the possibility of an incentive-laden deal (such as a $2.25-2.5 million base with incentives potentially escalating the value to $3.25-3.5 million). Would Walden be interested in this? Probably not. Would $500,000-750,000 "cripple" the Cardinals? Absolutely not, but it's at least worth bringing up when looking at a relief pitcher with a significant injury history—including arm health.