Prospects Worldwide

Merrill Kelly: A Mirage in the Desert or an Under-Appreciated Starter?

Written by: Danny Hacker
Follow him on Twitter:@theGREATdanny94
Follow Prospects Worldwide on Twitter:@ProspectsWorldW


Before having to undergo Thoratic Outlet Surgery, Merrill Kelly was one of the best starting pitchers in the National League during last year’s shortened season with a 2.58 ERA and a 0.989 WHIP in 31.1 Innings Pitched (5 Starts). Many people believed it to be a mirage, citing the short season along with Kelly’s mediocre 4.42 ERA, 1.315 WHIP and poor Savant rankings from 2019 but there is way more to the story than what reads on the stat sheet. How do we judge the 2020 season is the common question all offseason in regards to every player but in a case like Merrill Kelly, teams (and fantasy owners) are wondering which one they’re going to get; the one from 2019 or the one from 2020. To me, the answer is the 2020 version more so than the early 2019 version. Let’s find out why:

First, let’s look at the overall numbers between the last two seasons:

2019: 4.42 ERA, 4.51 FIP, 7.8 K/9, 2.8 BB/9, 9.0 H/9, 1.315 WHIP in 183.1 IP (32 Starts)

2020: 2.59 ERA, 3.99 FIP, 8.3 K/9, 1.4 BB/9, 7.5 H/9, 0.989 WHIP in 31.1 IP (5 Starts)

Obviously off the get go, you see that there is drastic improvement in most of the major categories while also bumping up his K/9 by 0.5 which is something you’d like to see as well. People point to the shortened season as a mirage but there actually were quite a few indications that Merrill Kelly was going to break out some in 2020 thanks to the end of 2019. For example, I tweeted this out in September 2019:

And this in December of 2019:

Merrill Kelly made some mechanical changes mid-2019 and as a result, it really helped. It also gave him a few extra ticks on his velocity putting him in the 94-95 mph range along with a few more RPM on his above average spin rate fastball (81st Percentile) which gave him a 9.0+ K/9 over that last five start span (35 K in 33.0 IP). Therefore going into 2020, he continued the adjustments and excelled obviously before having to undergo surgery and missing the rest of the season. The breakout 2020 wasn’t a mirage because of said indications that hinted at him doing a lot better than he had early on.

When looking at Kelly’s Savant data, you will notice some positive jumps in most of the relatively “important” data points of the Savant profile. In 2019, he was in the 17th Percentile of Exit Velocity vs the 47th Percentile in 2020. In 2019, he was in the 17th Percentiles of both xERA and xwOBA vs the 60th Percentile for both categories. In 2019, he was in the 15th Percentile for xBA vs the 46th Percentile in 2020. In 2019, he was in the 34th Percentile for xOBP vs the 81st Percentile in 2020. See the trend? It all equals Kelly’s improvement. In addition to the 2019 adjustments that hinted at this improved Kelly, why else was he so successful in 2020?

First, he was so successful in 2020 was because of the improvements he made to his pitch mix, primarily reducing his fastball usage drastically. In 2019, Merrill Kelly used his fastball 37.3% of the time and in 2020, it was 24.7%; a whopping 13.6% decrease from 2019. That allowed him to equally mix his pitches more often and more effectively to not be as predictable. In 2020, he threw every pitch of his five pitch mix at least 15.0% of the time which made each more impactful with his 65.1% Strike Percentage (59.2% First Pitch Strike percentage) which was up from 64% in 2019. Here is the graph of his pitch mixes in 2019 and 2020:


Merrill Kelly’s September of 2019 and improved pitch mix aren’t the only reasons he succeeded in 2020; another is the improvement of every pitch from a movement standpoint and therefore a quality results standpoint. The two biggest pitches Kelly overhauled and improved were his changeup and his sinker with a whole lot of red all around

The difference between Kelly’s 2019 changeup and 2020 changeup are drastically night and day. In 2019, the pitch was among the worst in vertical movement (-6″ of drop vs the average changeup) and was below average in horizontal movement (-1.1″ of drop vs the average changeup) which resulted in a .316 BA/.315 xBA, a 24.1% whiff percent and a 13.5% put away percent with a spin rate of 2,109 RPM.

In 2020, Merrill Kelly’s changeup became a legitimate weapon and one of the better changeups in the game in regards to horizontal movement and became league average in vertical movement. The pitch’s horizontal movement jumped to 2.7″ of break, or 20% more break, more than the average changeup (which placed him in the 89th percentile among the 285 pitchers that registered changeups on the Savant leaderboard) and the vertical movement of the pitch was -0.5″ of drop, or -2%, vs the average changeup. The results of that improvement allowed the pitch to result in a .292 BA/.226 xBA, a 38.6% whiff percent and a 36.8% put away percent with a spin rate of 1,999 RPM (less RPM on Changeup = better). By throwing the improved pitch just 2% more of the time from 13.4% to 15.4%, it made tremendous gains and became one of Kelly’s best pitches to get outs with (1st in both whiff percent and put away percent in 2020) and trailed only the curveball in number of strikeouts with it.

Next, we will look at Kelly’s sinker, the second most improved pitch in the arsenal. In 2019, the pitch had 0.9″ inches of drop, or 4%, more than the average sinker and -0.7″ of break, or -5%, less than the average sinker which resulted in a .306 BA/.328 xBA, a 16.2% whiff percent and a 16.7% put away percent with a spin rate of 2,313 RPM.

In 2020, the sinker improved to having 1.3″ of drop, or 6%, more than the average sinker and 1.2″ of break, or 8%, more than the average changeup which resulted in a .167 BA/.239 xBA, a 22.5% whiff percent and a 28.0% put away percent with a spin rate of 2,257 RPM. Yes the spin rate dropped a few RPM but it also is better to see sinkers with lesser RPM than a fastball. The sinker was the 2nd in put away percent and 3rd in whiff percent in 2020 as Kelly essentially doubled its usage from 9.7% to 17.5% as it became a much more effective pitch to use in the arsenal.

Kelly’s HR/9 stayed identical in 2020 vs 2019 (1.4 HR/9) and that isn’t necessarily a good thing because you ideally want to see a HR/9 around 1.0 or less. However it’s worth noting that MLB has changed the ball, “deadening” it in the process so a pitcher like Kelly is likely to improve in that category in 2021 as a result. It’s worth noting that on Kelly’s new changeup, there wasn’t a single fly ball hit off of it in 2020 vs 30.9% in 2019. In fact; in 2020, Kelly’s Fly Ball Percent decreased on every pitch except for the sinker which only went up 1.9% to 13% from 11.1% in 2019. That, along with the ball, also gives hope that Kelly will improve in 2021 while maintaining/improving on everything else.

Now obviously, all of this is a mute point if Kelly doesn’t stay healthy after surgery (which with this type does not have a good track record) but both the Diamondbacks and Kelly believe he is healthy and fully past the effects of the surgery. Per reports, and some Savant data, Kelly is hitting 94 mph like he was in 2020 with his fastball which is very promising. A lot of people are scared off because of the surgery but he is absolutely a major bargain right now as a result if you’re looking for a starter in real life or in fantasy baseball. He has struggled some this spring but seems to be just shaking off the rust after missing all of last September.

As the season winds closer, Merrill Kelly is a starter you will want to keep an eye on for both in fantasy and real life as teams look for starting pitching (aren’t they always?). He’s cost controlled for at least 2 more seasons ($4.25M this year and a $5.25M Club Option for 2022) meaning a team trading for him would get be able to add him without fear of breaking the budget. Kelly’s out to prove 2020 wasn’t just a mirage in the desert but rather show that he is a very good, and very underrated, starting pitcher surprising a lot of people in the process.


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