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Taking a Look At Our Rotation's Velocities

What can their velocities tell us about the playoffs?

San Francisco Giants v Arizona Diamondbacks Photo by Jennifer Stewart/Getty Images

It's a long season and we still have just over a month left. This is also a great time to take a look at the velocities of our starting pitchers. Often, changes in velocity end up being a sign of things to come and given the large sample of ~25-30 games for each pitcher, we can have a pretty good idea of how things are trending.

Keep in mind, that we're looking at a fairly small sample here, so we're going to focus on a month-by-month basis. Generally speaking, pitcher velocities increase as the season goes on, but that is mostly due to cold weather in March/April. I think the Dbacks are less affected by this, as we mostly play in warm(ish) weather in April.

I am only focusing on our starting rotation and on each pitcher's primary fastball (which is four-seam for everybody except Godley's sinker).

Zack Greinke

Greinke 4-Seam Fastball Velocity 2017

Greinke follows the standard pattern that is largely seen across the league for pitching velocity. It is even more important for Greinke as he started the season out considerably lower than where he was at last year. And even though he's increased his velocity over the course of the 2017 season, he's still averaging 90.95 MPH - a full 1.4 MPH lower than his fastball velocity in 2016.

This is both a good and a troubling sign for Greinke. The good news is that we are able to see Greinke dominate with diminished velocity, which could indicate success for years to come over his contract. That troubling sign is that this might indicate that Greinke's aging has started to kick in. This doesn't mean his FB will continue to decay quickly, but it is something to keep an eye out moving forward.

Concern for the playoffs: None as I can see it. Greinke's been dominant all season long and his velocity is trending in a positive direction. I don't see any element of him being hurt. He should be expected to be our top pitcher in the playoffs.

Robbie Ray

Ray 4-Seam Fastball Velocity 2017

At first glance, it seems like there might be reason to be concerned for Robbie Ray because of the ~1 MPH drop in August. And there is - but it's due to a concussion, not an arm injury (presumably).

There is only one game for Ray so far in August and that was his first game back from the concussion DL. It seems reasonable to me that his first game back after a few weeks on the DL would see his fastball about a tick lower. This is something we'll need to follow over the course of the rest of the season. Considering his velo was increasing positively before the concussion, I think the concern is mild at this point.

Concern for the playoffs: Mild. Robbie was trending up before the concussion and concussions don't seem to have lingering effects in baseball. It's something to keep an eye out in September but he should be good as our #2.

Taijuan Walker

Walker 4-Seam Fastball Velocity 2017

Walker is a bit confusing and I honestly don't know how to interpret it. And it's not like that June sample (2 MPH higher than May, July, August) is only 1 game:

Walker 4-seam Fastball Velocity, Per Game

Looking at the game-by-game log, it looks like there is a slight downward trend for Walker with some spikes both up and down. To me, it looks like we're dealing with a pitcher that is still struggling with mechanics and his mentality on the mound. We've seen him absolutely dominate lineups but we've also seen him look very sheepish on the mound, too.

I was worried when I watched Walker during the Astros game. He looks really out of it and his fastball velocity had dropped to an average of 92.4 MPH - his lowest on the season. I was concerned that he might have had some sort of injury, but he has since rebounded with two solid games against the Mets (game score: 60) and Giants (game score: 62) and higher velocities.

Don't get me wrong, Walker has still been fairly solid this season. He's done a great job of suppressing home runs and managing batted ball contact. On the other hand, his strikeout rate has dropped and his walk rate has increased since last season, both of which are the wrong direction for a developing pitcher. Walker could be hiding an injury or he could be going through the growing pains of a very young pitcher. It's something that we should keep an eye on going forward, both this year and next.

Concern for the playoffs: Medium. I don't think Walker is super close to an injury or wearing down by the playoffs, but his seemingly inconsistent mechanics could be a problem in a starting role in the playoffs. Walker seems like he would be prime fit a bullpen role in the playoffs if he keeps his velocity up. He would also fly as our #4/#5 if needed.

Patrick Corbin

Corbin 4-Seam Fastball Velocity 2017

Corbin is baffling. At first glance, the velocity graph seems to show a pitcher that is wearing down as the season goes on. And his latest game against the Giants showed him only averaging 91.8 MPH, clearly his lowest on the season (though, it might be an error as that game was a clear outlier from the rest of the season).

Where it gets confusing is that Corbin's downward projection in velocity is that it pretty much correlates directly with his improved performance over the last 15 games. And considering that he's already had Tommy John (which greatly increases odds of needing it again), there is some concern that despite his improved performance since June 8th, there might still be an injury risk at play.

On the other hand, I think it might actually be intentionally. As Diamondhacks noticed a few days ago, it appeared that Corbin was getting ahead of batters much more frequently. And he was right: Corbin was throwing first strikes nearly 10% more often than he was before. Perhaps Corbin has sacrificed some velocity in order to locate better?

Corbin Heatmap, before/after 6/8/17

It might appear to you that Corbin is throwing less strikes than he was before - and you'd be right - despite what I said above about him locating better. But command =/= more strikes; it means throwing where you want the pitch to be. Notice how Corbin has dramatically lowered the amount of pitches he is throwng in the middle part of the plate. And he was doing this while getting ahead of batters more often.

But Corbin is still a cautionary tale. He's already surpassed his inning total from last year and this is his second year since his TJ surgery, so there could absolutely be fatigue setting in for Corbin. This is something I will keep an eye on.

Concern for the Playoffs: Medium-High. Considering his inning totals and his TJ surgery, I think there is certainly more risk for Corbin in the playoffs than usual. It seems like the team has been pushing him deeper into games lately - and I think he's deserved it with his strong performances - but I would like to see them ease Corbin back over September if he is indeed showing signs of fatigue. If Corbin is still feeling strong and dominating like he is, he will be a #3/#4 for us in the playoffs.

Zack Godley

Godley Sinker Velocity 2017

As sad as it is to say, Godley is the most concerning out of our rotation right now. Godley is already 14 innings higher than he pitched in the MLB and AAA combined last year and it appears that fatigue might be setting in for Godley. It's not a dramatic drop - less than 1 MPH since he became a starter - so I don't think it's an injury at play here.

We've seen how good Godley can be (I mean, I couldn't stop writing about him) but he hasn't looked as strong in his last few starts. My guess is that fatigue is starting to hit Godley which could have an impact for him in the playoffs. If the team views him as one of our starters in the playoffs, then it might be wise to hold him back a bit through September.

Concern for the Playoffs: High. It seems clear that fatigue is hitting Godley and I don't think Godley has the command to get by with lessened stuff in a playoff setting. Godley might have to shift to a bullpen role in the playoffs not because of stuff, but because of fatigue. He could be a very valuable inning eater in a bullpen role, however, if his newly-found 2017 "stuff" translates over.